Annual report pursuant to Section 13 and 15(d)

Fair Value Measurement of Plan Assets Using Unobservable Inputs (Detail)

v2.4.0.6
Fair Value Measurement of Plan Assets Using Unobservable Inputs (Detail) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2011
Dec. 31, 2010
Actual Return on Assets:    
Ending Balance $ 22,837 $ 20,325
Fair Value, Inputs, Level 3
    
Defined Benefit Plan Disclosure [Line Items]    
Beginning Balance 4,314 3,180
Actual Return on Assets:    
Assets Held at End of Year 397 401
Assets Sold During the Year 30 24
Purchases 1,128 1,053
Sales (744) (344)
Settlements      
Transfers Into (Out of) Level 3      
Ending Balance 5,125 4,314
Fair Value, Inputs, Level 3 | Corporate Bonds
    
Defined Benefit Plan Disclosure [Line Items]    
Beginning Balance 193 201
Actual Return on Assets:    
Assets Held at End of Year (14) (5)
Assets Sold During the Year 3 13
Purchases 57 41
Sales (159) (57)
Settlements      
Transfers Into (Out of) Level 3      
Ending Balance 80 193
Fair Value, Inputs, Level 3 | Hedge Funds
    
Defined Benefit Plan Disclosure [Line Items]    
Beginning Balance 2,023 1,284
Actual Return on Assets:    
Assets Held at End of Year 122 129
Assets Sold During the Year 22 10
Purchases 757 711
Sales (181) (111)
Settlements      
Transfers Into (Out of) Level 3      
Ending Balance 2,743 2,023
Fair Value, Inputs, Level 3 | Real Estate
    
Defined Benefit Plan Disclosure [Line Items]    
Beginning Balance 789 550
Actual Return on Assets:    
Assets Held at End of Year 144 100
Assets Sold During the Year 5  
Purchases 150 152
Sales (140) (13)
Settlements      
Transfers Into (Out of) Level 3      
Ending Balance 948 789
Fair Value, Inputs, Level 3 | Private Equity
    
Defined Benefit Plan Disclosure [Line Items]    
Beginning Balance 1,309 1,145
Actual Return on Assets:    
Assets Held at End of Year 145 177
Assets Sold During the Year   1
Purchases 164 149
Sales (264) (163)
Settlements      
Transfers Into (Out of) Level 3      
Ending Balance $ 1,354 $ 1,309