Earnings Per Common Share (EPS) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2016		Jun. 30, 2015		Jun. 30, 2016		Jun. 30, 2015
Basic and diluted:
Net income	$ 2,015.0		$ 1,473.0		$ 3,441.0		$ 2,998.0
Preferred dividends	(19.0)		(20.0)		(40.0)		(20.0)
Net income available to common stockholders - basic	1,996.0		1,453.0		3,401.0		2,978.0
Net income available to common stockholders - diluted	1,996.0		1,453.0		3,401.0		2,978.0
Earnings allocated to participating share awards	(17.0)		(11.0)		(28.0)		(22.0)
Net income attributable to common shareholders	$ 1,979.0		$ 1,442.0		$ 3,373.0		$ 2,956.0
Denominator:
Basic	938.0		1,009.0		949.0		1,013.0
Add: Weighted-average stock options	3.0		4.0		3.0		5.0
Diluted	941.0		1,013.0		952.0		1,018.0
Earnings Per Common Share, Basic (Note 15) [Abstract]
Net income attributable to common shareholders	$ 2.11	[1]	$ 1.43	[1]	$ 3.55	[2]	$ 2.92	[2]
Earnings Per Common Share, Diluted (Note 15) [Abstract]
Net income attributable to common shareholders	$ 2.1	[3]	$ 1.42	[3]	$ 3.54	[4]	$ 2.9	[4]
Earnings Per Common Share (Textuals) [Abstract]
Subordinated debentures	$ 750.0				$ 750.0
Subordinated debt issuance year	2006
Subordinated debt maturity year	2036
Stock options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per Share, amount	2.5		0.6		1.7		0.5

[1] Represents net income less ( i ) earnings allocated to participating share awards of $ 17 million and $ 11 million for the three months ended June 30 , 2016 and 2015 , respectively, and (ii) dividends on preferred shares of $ 19 million and $ 20 million for the three months ended June 30 , 2016 and 2015 , respectively.

[2] Represents net income less ( i ) earnings allocate d to participating share awards of $ 28 million and $ 22 million for the six months ended June 30 , 2016 and 2015 , respectively, and (ii) dividends on preferred shares of $ 40 million and $ 20 million for the six months ended June 30 , 2016 and 2015 , respectively.

[3] Represents net income less ( i ) earnings allocated to participating share awards of $ 17 million and $ 11 million for the three months ended June 30 , 2016 and 2015 , respectively, and (ii) dividends on preferred shares of $ 19 million and $ 20 million for the three months ended June 30 , 2016 and 2015 , respectively.

[4] Represents net income less ( i ) earnings allocate d to participating share awards of $ 28 million and $ 22 million for the six months ended June 30 , 2016 and 2015 , respectively, and (ii) dividends on preferred shares of $ 40 million and $ 20 million for the six months ended June 30 , 2016 and 2015 , respectively.