Shareholders' Equity - Components of Accumulated Other Comprehensive Income (Parenthetical) (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
OTTI Gains (Losses) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Tax on change in other comprehensive income (loss) before reclassifications	$ 1	$ 2	$ (1)	$ 2
Tax on reclassification from accumulated other comprehensive income	0	0	(1)	0
Unrealized Gains (Losses) on Investments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Tax on change in other comprehensive income (loss) before reclassifications	(164)	186	(272)	124
Tax on reclassification from accumulated other comprehensive income	6	(5)	(1)	(5)
Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Tax on change in other comprehensive income (loss) before reclassifications	0	0	0	1
Tax on reclassification from accumulated other comprehensive income	0	0	0	(2)
Pension Liability [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Tax on change in other comprehensive income (loss) before reclassifications	0	(18)	0	(18)
Tax on reclassification from accumulated other comprehensive income	(4)	(4)	(7)	(7)
Foreign Currency Translation [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Tax on change in other comprehensive income (loss) before reclassifications	0	0	0	0
Tax on reclassification from accumulated other comprehensive income	$ 0	$ 0	$ 0	$ 0