CONSOLIDATED STATEMENT OF CHANGES IN EQUITY - USD ($) $ in Millions	Total		Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Loss [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Reclassification to accumulated other comprehensive loss of cumulative effect adjustment to initially apply new accounting guidance for financial liabilities measured under the fair value option, net of tax	$ 0	[1]				$ 0	$ 0
Reclassification from retained earnings of cumulative effect adjustment to initially apply new accounting guidance for financial liabilities measured under the fair value option, net of tax	0	[1]				0	0
Balance at beginning of period at Dec. 31, 2015			$ 1,265
Balance at end of period at Mar. 31, 2016	20,896		1,265
Balance at beginning of period (As Previously Reported [Member]) at Dec. 31, 2015						1,498	(407)
Balance at beginning of period at Dec. 31, 2015				$ 0	$ 18,169	1,498	(407)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Employee benefit plans					(2)
Net income	154					154
Cash dividends declared on preferred stock						(14)
Other comprehensive income, net of tax	233						233
Balance at end of period at Mar. 31, 2016	19,631			0	18,167	1,638	(174)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Reclassification to accumulated other comprehensive loss of cumulative effect adjustment to initially apply new accounting guidance for financial liabilities measured under the fair value option, net of tax	174	[1]				(174)	174
Reclassification from retained earnings of cumulative effect adjustment to initially apply new accounting guidance for financial liabilities measured under the fair value option, net of tax	174	[1]				(174)	174
Balance at beginning of period at Dec. 31, 2016	20,355		1,265
Balance at end of period at Mar. 31, 2017	20,674		$ 1,265
Balance at beginning of period (As Previously Reported [Member]) at Dec. 31, 2016						1,560	(618)
Balance at beginning of period at Dec. 31, 2016	19,090			0	18,148	1,386	(444)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Employee benefit plans					(6)
Net income	296					296
Cash dividends declared on preferred stock						0
Other comprehensive income, net of tax	29						29
Balance at end of period at Mar. 31, 2017	$ 19,409			$ 0	$ 18,142	$ 1,682	$ (415)

[1] See Note 19, "New Accounting Pronouncements," for additional discussion.