Earnings Per Common Share (EPS) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2018		Sep. 30, 2017		Sep. 30, 2018		Sep. 30, 2017
Basic and diluted:
Net income	$ 1,654		$ 1,359		$ 4,911		$ 3,954
Preferred dividends	(20)		(21)		(61)		(61)
Net Income Loss Available to Common Shareholders	1,634		1,338		4,850		3,893
Earnings allocated to participating share awards	(13)		(11)		(38)		(32)
Net Income Attributable to Common Shareholders	$ 1,621		$ 1,327		$ 4,812		$ 3,861
Denominator:
Basic	858.0		878.0		859.0		889.0
Add: Weighted-average stock options	2.0		3.0		2.0		3.0
Diluted	860.0		881.0		861.0		892.0
Earnings Per Common Share, Basic (Note 15) [Abstract]
Net income attributable to common shareholders	$ 1.89	[1]	$ 1.51	[1]	$ 5.6	[2]	$ 4.34	[2]
Earnings Per Common Share, Diluted (Note 15) [Abstract]
Net income attributable to common shareholders	$ 1.88	[1]	$ 1.51	[1]	$ 5.59	[2]	$ 4.33	[2]
Stock options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per Share, amount	0.7		0.5		0.7		0.8

[1] Rep resents net income less (i) earnings allocated to participating share awards of $ 13 million and $ 11 million for the three months ended September 30 , 2018 and 2017 , respectively, and (ii) dividends on preferred shares of $ 20 million and $ 21 million for the three months ended September 30 , 2018 and 2017 , respectively .

[2] Represents net income less (i) earnings allocated to participating share awards of $ 38 million and $ 32 million for the nine months ended September 30 , 2018 and 2017 , respectively, and (ii) dividends on preferred shares of $ 61 million for both the nine months ended September 30 , 2018 and 2017 .