CONSOLIDATED STATEMENT OF CHANGES IN EQUITY (UNAUDITED) - 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
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Preferred stock issuance			1,265
Preferred stock redemption			(1,265)
Balance at end of period at Sep. 30, 2016	20,977		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					(12)
Net income	166					166
Cash dividends declared on preferred stock						(29)
Other comprehensive income, net of tax	327						327
Balance at end of period at Sep. 30, 2016	19,712			0	18,157	1,635	(80)
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
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Preferred stock issuance			0
Preferred stock redemption			0
Balance at end of period at Sep. 30, 2017	20,998		$ 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					(19)
Net income	594					594
Cash dividends declared on preferred stock						(38)
Other comprehensive income, net of tax	106						106
Balance at end of period at Sep. 30, 2017	$ 19,733			$ 0	$ 18,129	$ 1,942	$ (338)

[1] See Note 20, "New Accounting Pronouncements," for additional discussion.