Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disclosure of quarterly financial data
Total revenues net of interest expense	$ 9,351	$ 8,751	$ 7,675	$ 10,310	$ 11,365	$ 10,989	$ 10,838	$ 10,364	$ 36,087	$ 43,556	$ 40,338
Pretax income	1,858	1,364	622	452	1,986	2,266	2,219	1,958	4,296	8,429	8,122
Net income (loss)	$ 1,438	$ 1,073	$ 257	$ 367	$ 1,693	$ 1,755	$ 1,761	$ 1,550	$ 3,135	$ 6,759	$ 6,921
Earnings per Common Share
Net income attributable to common shareholders (in dollars per share)	$ 1.76	$ 1.31	$ 0.29	$ 0.41	$ 2.04	$ 2.09	$ 2.07	$ 1.81
Earnings per Common Share
Net income attributable to common shareholders (in dollars per share)	1.76	1.30	0.29	0.41	2.03	2.08	2.07	1.80
Cash dividends declared per common share (in dollars per share)	$ 0.43	$ 0.43	$ 0.43	$ 0.43	$ 0.43	$ 0.43	$ 0.39	$ 0.39	$ 1.72	$ 1.64	$ 1.48