Income Taxes (Income Taxes and Shareholders' Equity) (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current taxes:
Federal	$ 4	$ 4	$ 0
State	0	1	1
Foreign	0	0	2
Deferred taxes:
Federal	945	(8)	97
Foreign	(5)	2	9
Provision (benefit) for income taxes	944	(1)	109
Income tax effects allocated directly to equity [Abstract]
Change in unrealized gains and losses on AFS securities	(1)	8	(30)
Change in AFS securities with OTTI	1	5	0
Change in foreign currency translation	21	1	(14)
Share-based compensation	0	0	9
Total income taxes charged (credited) to shareholders' equity	21	14	(35)
Total effect of income taxes	$ 965	$ 13	$ 74

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