Earnings Per Common Share (EPS) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2018		Jun. 30, 2017		Jun. 30, 2018		Jun. 30, 2017
Basic and diluted:
Net income	$ 1,623.0		$ 1,344.0		$ 3,257.0		$ 2,595.0
Preferred dividends	(20.0)		(19.0)		(41.0)		(40.0)
Net Income Loss Available to Common Shareholders	1,603.0		1,325.0		3,216.0		2,555.0
Net income attributable to common shareholders	1,603.0		1,325.0		3,216.0		2,555.0
Earnings allocated to participating share awards	(12.0)		(11.0)		(25.0)		(21.0)
Net Income Attributable to Common Shareholders	$ 1,591.0		$ 1,314.0		$ 3,191.0		$ 2,534.0
Denominator:
Basic	860.0		890.0		859.0		895.0
Add: Weighted-average stock options	2.0		3.0		3.0		3.0
Diluted	862.0		893.0		862.0		898.0
Earnings Per Common Share, Basic (Note 15) [Abstract]
Net income attributable to common shareholders	$ 1.85	[1]	$ 1.48	[1]	$ 3.71	[2]	$ 2.83	[2]
Earnings Per Common Share, Diluted (Note 15) [Abstract]
Net income attributable to common shareholders	$ 1.84	[1]	$ 1.47	[1]	$ 3.7	[2]	$ 2.82	[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		1.2		0.7		1.2

[1] Rep resents net income less (i) earnings allocated to participating share awards of $ 12 million and $ 11 million for the three months ended June 30 , 2018 and 2017 , respectively, and (ii) dividends on preferred shares of $ 20 million and $ 19 million for the three months ended June 30 , 2018 and 2017 , respectively .

[2] Represents net income less (i) earnings allocated to participating share awards of $ 25 million and $ 21 million for the six months ended June 30 , 2018 and 2017 , respectively, and (ii) dividends on preferred shares of $ 41 million and $ 40 million for the six months ended June 30 , 2018 and 2017 , respectively .