Earnings Per Common Share (EPS) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Basic and diluted:
Net income		$ 1,634	$ 1,251
Preferred dividends		(21)	(21)
Net income available to common stockholders - basic		1,613	1,230
Net income available to common stockholders - diluted		1,613	1,230
Earnings allocated to participating share awards		(13)	(10)
Net income attributable to common shareholders		$ 1,600	$ 1,220
Denominator:
Basic		859.0	899.0
Add: Weighted-average stock options		2.0	4.0
Diluted		861.0	903.0
Earnings Per Common Share, Basic (Note 15) [Abstract]
Net income attributable to common shareholders	[1]	$ 1.86	$ 1.36
Earnings Per Common Share, Diluted (Note 15) [Abstract]
Net income attributable to common shareholders	[1]	$ 1.86	$ 1.35
Stock options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per Share, amount		0.6	1.2

[1] Rep resents net income less (i) earnings allocated to participating share awards of $ 13 million and $ 10 million for the three months ended March 31 , 2018 and 2017 , respectively, and (ii) dividends on preferred shares of $ 21 million for both the three months ended March 31 , 2018 and 2017 .