Income Taxes (Income Taxes and Shareholders' Equity) (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Current taxes:
Federal	$ 0	$ 0	$ 4
State	2	1	0
Deferred taxes:
Federal	0	(1)	945
Foreign	0	0	(5)
Provision (benefit) for income taxes	2	0	944
Income taxes charged (credited) to shareholders' equity related to:
Change in unrealized gains (losses) on AFS securities	0	5	(1)
Change in AFS securities with OTTI	0	0	1
Change in foreign currency translation	0	0	21
Total income taxes charged (credited) to shareholders' equity	0	5	21
Total effect of income taxes	$ 2	$ 5	$ 965

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