Earnings Per Common Share (EPS) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016
Basic and diluted:
Net income		$ 1,237	$ 1,426
Preferred dividends		(21)	(21)
Net income available to common stockholders - basic		1,216	1,405
Net income available to common stockholders - diluted		1,216	1,405
Earnings allocated to participating share awards		(10)	(11)
Net income attributable to common shareholders		$ 1,206	$ 1,394
Denominator:
Basic		899.0	961.0
Add: Weighted-average stock options		4.0	2.0
Diluted		903.0	963.0
Earnings Per Common Share, Basic (Note 15) [Abstract]
Net income attributable to common shareholders	[1]	$ 1.34	$ 1.45
Earnings Per Common Share, Diluted (Note 15) [Abstract]
Net income attributable to common shareholders	[2]	$ 1.34	$ 1.45
Stock options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per Share, amount		1.2	1.5

[1] Represents net income less (i) earnings allocated to participating share awards of $ 10 million and $ 11 million for the three months ended March 31 , 2017 and 2016 , respectively, and (ii) dividends on preferred shares of $ 21 million for both the three months ended March 31 , 2017 and 2016 .

[2] Represents net income less (i) earnings allocated to participating share awards of $ 10 million and $ 11 million for the three months ended March 31 , 2017 and 2016 , respectively, and (ii) dividends on preferred shares of $ 21 million for both the three months ended March 31 , 2017 and 2016 .