Earnings Per Common Share (EPS) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2019		Jun. 30, 2018		Jun. 30, 2019		Jun. 30, 2018
Basic and diluted:
Net income	$ 1,761		$ 1,623		$ 3,311		$ 3,257
Preferred dividends	(19)		(20)		(40)		(41)
Net Income (Loss) Available to Common Stockholders, Basic	1,742		1,603		3,271		3,216
Earnings allocated to participating share awards	(13)		12		24		(25)
Net Income Attributable to Common Shareholders	$ 1,729		$ 1,591		$ 3,247		$ 3,191
Denominator:
Basic (in shares)	834.0		860.0		837.0		859.0
Add: Weighted-average stock options (in shares)	2.0		2.0		2.0		3.0
Diluted (in shares)	836.0		862.0		839.0		862.0
Basic EPS (in dollars per share)	$ 2.07	[1]	$ 1.85	[1]	$ 3.88	[2]	$ 3.71	[2]
Diluted EPS (in dollars per share)	$ 2.07	[1]	$ 1.84	[1]	$ 3.87	[2]	$ 3.70	[2]
Stock options [Member]
Denominator:
Antidilutive securities excluded from computation of earnings per share, (in shares)	0.4		0.7		0.4		0.7

[1] Represents net income less (i) earnings allocated to participating share awards of $13 million and $12 million for the three months ended June 30, 2019 and 2018, respectively, and (ii) dividends on preferred shares of $19 million and $20 million for the three months ended June 30, 2019 and 2018, respectively.

[2] Represents net income less (i) earnings allocated to participating share awards of $24 million and $25 million for the six months ended June 30, 2019 and 2018, respectively, and (ii) dividends on preferred shares of $40 million and $41 million for the six months ended June 30, 2019 and 2018, respectively.