Earnings Per Common Share (EPS) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2017		Sep. 30, 2016		Sep. 30, 2017		Sep. 30, 2016
Basic and diluted:
Net income	$ 1,356.0		$ 1,142.0		$ 3,933.0		$ 4,583.0
Preferred dividends	(21.0)		(21.0)		(61.0)		(61.0)
Net income available to common stockholders - basic	1,335.0		1,121.0		3,872.0		4,522.0
Net income available to common stockholders - diluted	1,335.0		1,121.0		3,872.0		4,522.0
Earnings allocated to participating share awards	(11.0)		(9.0)		(32.0)		(37.0)
Net income attributable to common shareholders	$ 1,324.0		$ 1,112.0		$ 3,840.0		$ 4,485.0
Denominator:
Basic	878.0		920.0		889.0		940.0
Add: Weighted-average stock options	3.0		3.0		3.0		3.0
Diluted	881.0		923.0		892.0		943.0
Earnings Per Common Share, Basic (Note 15) [Abstract]
Net income attributable to common shareholders	$ 1.51	[1]	$ 1.21	[1]	$ 4.32	[2]	$ 4.77	[2]
Earnings Per Common Share, Diluted (Note 15) [Abstract]
Net income attributable to common shareholders	$ 1.5	[1]	$ 1.2	[1]	$ 4.3	[2]	$ 4.76	[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	0.5		3.2		0.8		2.2

[1] Represents net income less (i) earnings allocated to participating share awards of $ 11 million and $ 9 million for the three months ended September 30 , 2017 and 2016 , respectively, and (ii) dividends on preferred shares of $ 21 million for both the three months ended September 30 , 2017 and 2016 .

[2] Represents net income less (i) earnings allocated to participating share awards of $ 32 million and $ 37 million for the nine months ended September 30 , 2017 and 2016 , respectively, and (ii) dividends on preferred shares of $ 61 million for both the nine months ended September 30 , 2017 and 2016 .