Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of quarterly financial data
Total revenues net of interest expense		$ 10,474	$ 10,144	$ 10,002	$ 9,718	$ 9,707	$ 9,290	$ 9,172	$ 8,709	$ 40,338	$ 36,878	$ 35,438
Pretax income		1,831	2,118	2,091	2,082	1,798	1,831	1,957	1,839	8,122	7,425	8,042
Net income		$ 2,010	$ 1,654	$ 1,623	$ 1,634	$ (1,206)	$ 1,359	$ 1,344	$ 1,251	$ 6,921	$ 2,748	$ 5,375
Earnings per Common Share
Basic	[1]									$ 7.93	$ 3	$ 5.63
Net income attributable to common shareholders	[2]	$ 2.33	$ 1.89	$ 1.85	$ 1.86	$ (1.42)	$ 1.51	$ 1.48	$ 1.36
Earnings per Common Share
Diluted	[1]									7.91	2.99	5.61
Net income attributable to common shareholders	[2]	2.32	1.88	1.84	1.86	(1.42)	1.51	1.47	1.35
Cash dividends declared per common share		$ 0.39	$ 0.39	$ 0.35	$ 0.35	$ 0.35	$ 0.35	$ 0.32	$ 0.32	$ 1.48	$ 1.34	$ 1.22

[1] Represents net income less (i) earnings allocated to participating share awards of $ 54 million, $ 21 million and $ 43 million for the years ended December 31, 2018 , 2017 and 2016 , respectively, and (ii) dividends on preferred shares of $ 80 millio n, $ 81 million and $ 80 million for the years ended December 31, 2018 , 2017 and 2016 , r e s p e c t i v e l y .

[2] Represents net income, less (i) earnings allocated to participating share awards of $ 16 million, $ 13 million, $ 12 million and $ 13 million for the quarters ended December 31, September 30, June 30 and March 31, 2018 , respectively, and $ 2 million, $ 11 million, $ 11 million and $ 10 million for the quarters ended December 31, September 30, June 30 and March 31, 2017 , respectively, and (ii) dividend s on preferred shares of $ 19 million, $ 20 million, $ 20 million and $ 21 million for the quarters ended December 31, September 30, June 30 and March 31, 2018 , respectively, and $ 20 million, $ 21 million, $ 19 million and $ 21 million for the quarters ended December 31, September 30, June 30 and March 31, 2017 , respectively.