Quarterly Financial Data (Unaudited) (Details)		3 Months Ended								12 Months Ended
		Dec. 31, 2017 USD ($) $ / shares	Sep. 30, 2017 USD ($) $ / shares	Jun. 30, 2017 USD ($) $ / shares	Mar. 31, 2017 USD ($) $ / shares	Dec. 31, 2016 USD ($) $ / shares	Sep. 30, 2016 USD ($) $ / shares	Jun. 30, 2016 USD ($) $ / shares	Mar. 31, 2016 USD ($) $ / shares	Dec. 31, 2017 USD ($) $ / shares	Dec. 31, 2016 USD ($) $ / shares	Dec. 31, 2015 USD ($) $ / shares
Disclosure of quarterly financial data
Total revenues net of interest expense | $		$ 8,839,000,000	$ 8,436,000,000	$ 8,307,000,000	$ 7,889,000,000	$ 8,022,000,000	$ 7,774,000,000	$ 8,235,000,000	$ 8,088,000,000	$ 33,471,000,000	$ 32,119,000,000	$ 32,818,000,000
Pretax income | $		1,821,000,000	1,827,000,000	1,949,000,000	1,817,000,000	1,161,000,000	1,735,000,000	3,016,000,000	2,184,000,000	7,414,000,000	8,096,000,000	7,938,000,000
Net income | $		$ (1,197,000,000)	$ 1,356,000,000	$ 1,340,000,000	$ 1,237,000,000	$ 825,000,000	$ 1,142,000,000	$ 2,015,000,000	$ 1,426,000,000	$ 2,736,000,000	$ 5,408,000,000	$ 5,163,000,000
Earnings per Common Share
Basic | $ / shares	[1]									$ 2.98	$ 5.67	$ 5.07
Net income attributable to common shareholders | $ / shares		$ (1.41)	$ 1.51	$ 1.47	$ 1.34	$ 0.88	$ 1.21	$ 2.11	$ 1.45
Earnings per Common Share
Diluted | $ / shares										2.97	5.65	5.05
Net income attributable to common shareholders | $ / shares		(1.41)	1.5	1.47	1.34	0.88	1.2	2.1	1.45
Cash dividends declared per common share | $ / shares		$ 0.35	$ 0.35	$ 0.32	$ 0.32	$ 0.32	$ 0.32	$ 0.29	$ 0.29	$ 1.34	$ 1.22	$ 1.13
Common share price:
High | $		100.53	90.77	85.39	82	75.74	66.71	67.34	68.18
Low | $		90.04	83.33	75.51	74.74	59.5	58.25	57.15	50.27

[1] Represents net income less (i) earnings allocated to participating share awards of $ 21 million, $ 43 million and $ 38 million for the years ended December 31, 2017 , 2016 and 2015 , respectively, and (ii) dividends on preferred shares of $ 81 million, $ 80 million and $ 62 million for the years ended December 31, 2017 , 2016 and 2015 , respectively.