Earnings Per Common Share (EPS) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2019		Sep. 30, 2018		Sep. 30, 2019		Sep. 30, 2018
Basic and diluted:
Net income	$ 1,755		$ 1,654		$ 5,066		$ 4,911
Preferred dividends	(21)		(20)		(61)		(61)
Net income available to common shareholders	1,734		1,634		5,005		4,850
Earnings allocated to participating share awards	(11)		(13)		(35)		(38)
Net Income Attributable to Common Shareholders	$ 1,723		$ 1,621		$ 4,970		$ 4,812
Denominator:
Basic: Weighted-average common stock (in shares)	825,000,000		858,000,000		833,000,000		859,000,000
Add: Weighted-average stock options (in shares)	2,000,000		2,000,000		2,000,000		2,000,000
Diluted (in shares)	827,000,000		860,000,000		835,000,000		861,000,000
Basic EPS (in dollars per share)	$ 2.09	[1]	$ 1.89	[1]	$ 5.97	[2]	$ 5.60	[2]
Diluted EPS (in dollars per share)	$ 2.08	[1]	$ 1.88	[1]	$ 5.95	[2]	$ 5.59	[2]
Stock options [Member]
Denominator:
The dilutive effect of securities excluded from the calculation of earnings per share (in shares)	0		700,000		300,000		700,000

[1] Represents net income less (i) earnings allocated to participating share awards of $11 million and $13 million for the three months ended September 30, 2019 and 2018, respectively, and (ii) dividends on preferred shares of $21 million and $20 million for the three months ended September 30, 2019 and 2018, respectively.

[2] Represents net income less (i) earnings allocated to participating share awards of $35 million and $38 million for the nine months ended September 30, 2019 and 2018, respectively, and (ii) dividends on preferred shares of $61 million for both the nine months ended September 30, 2019 and 2018.