Income Taxes (Income Taxes and Shareholders' Equity) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Current taxes:
Federal	$ 0	$ 0	$ 0
State	0	2	1
Deferred taxes:
Federal	0	0	(1)
Foreign	0	0	0
Provision (benefit) for income taxes	0	2	0
Income taxes charged (credited) to shareholders' equity related to:
Change in unrealized gains (losses) on AFS securities	0	0	5
Change in AFS securities with OTTI	0	0	0
Change in foreign currency translation	0	0	0
Total income taxes charged (credited) to shareholders' equity	0	0	5
Total effect of income taxes	$ 0	$ 2	$ 5