Shareholders' Equity - Components of Accumulated Other Comprehensive Income (Parenthetical) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
OTTI Gains (Losses) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Tax on change in other comprehensive income (loss) before reclassifications	$ (4)	$ 13	$ (8)
Tax on reclassification from accumulated other comprehensive income	3	(8)	0
Unrealized Gains (Losses) on Investments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Tax on change in other comprehensive income (loss) before reclassifications	(133)	313	(132)
Tax on reclassification from accumulated other comprehensive income	16	(31)	10
Discontinued Operations [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Tax on change in other comprehensive income (loss) before reclassifications	0	0	(3)
Tax on reclassification from accumulated other comprehensive income	0	0	16
Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Tax on change in other comprehensive income (loss) before reclassifications	0	1	1
Tax on reclassification from accumulated other comprehensive income	0	(2)	0
Pension Liability [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Tax on change in other comprehensive income (loss) before reclassifications	9	16	132
Tax on reclassification from accumulated other comprehensive income	(15)	(11)	(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
Tax on reclassification from accumulated other comprehensive income	$ 0	$ 0	$ 0