Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of quarterly financial data
Total revenues net of interest expense		$ 11,365	$ 10,989	$ 10,838	$ 10,364	$ 10,474	$ 10,144	$ 10,002	$ 9,718	$ 43,556	$ 40,338	$ 36,878
Pretax income		1,986	2,266	2,219	1,958	1,831	2,118	2,091	2,082	8,429	8,122	7,425
Net Income (Loss) Attributable to Parent		$ 1,693	$ 1,755	$ 1,761	$ 1,550	$ 2,010	$ 1,654	$ 1,623	$ 1,634	$ 6,759	$ 6,921	$ 2,748
Earnings per Common Share
Basic (in dollars per share)	[1]									$ 8.00	$ 7.93	$ 3.00
Net income attributable to common shareholders		$ 2.04	$ 2.09	$ 2.07	$ 1.81	$ 2.33	$ 1.89	$ 1.85	$ 1.86
Earnings per Common Share
Diluted (in dollars per share)	[1]									7.99	7.91	2.99
Net income attributable to common shareholders		2.03	2.08	2.07	1.80	2.32	1.88	1.84	1.86
Cash dividends declared per common share (in dollars per share)		$ 0.43	$ 0.43	$ 0.39	$ 0.39	$ 0.39	$ 0.39	$ 0.35	$ 0.35	$ 1.64	$ 1.48	$ 1.34

[1] Represents net income less (i) earnings allocated to participating share awards of $47 million, $54 million and $21 million for the years ended December 31, 2019, 2018 and 2017, respectively, and (ii) dividends on preferred shares of $81 million, $80 million and $81 million for the years ended December 31, 2019, 2018 and 2017, respectively.