Quarterly report pursuant to Section 13 or 15(d)

Changes in Level 3 Instruments Measured on a Recurring Basis (Detail)

v3.8.0.1
Changes in Level 3 Instruments Measured on a Recurring Basis (Detail) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning Balance $ 6 $ 13
Transfers into (out of) Level 3 0 0
Net realized and unrealized gains (losses):    
Included in earnings (in investment income and other) (3) (2)
Included in accumulated other comprehensive income (pre-tax) 0 0
Purchases 0 0
Sales 0 0
Ending Balance 3 11
Marketable Securities    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning Balance 0 0
Transfers into (out of) Level 3 0 0
Net realized and unrealized gains (losses):    
Included in earnings (in investment income and other) 0 0
Included in accumulated other comprehensive income (pre-tax) 0 0
Purchases 0 0
Sales 0 0
Ending Balance 0 0
Other Non-Current Investments    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning Balance 6 13
Transfers into (out of) Level 3 0 0
Net realized and unrealized gains (losses):    
Included in earnings (in investment income and other) (3) (2)
Included in accumulated other comprehensive income (pre-tax) 0 0
Purchases 0 0
Sales 0 0
Ending Balance $ 3 $ 11