Stockholders' Equity - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	3 Months Ended			6 Months Ended	9 Months Ended
	May. 31, 2015	Sep. 30, 2015	Mar. 31, 2015	Sep. 30, 2014	Jun. 30, 2015	Sep. 30, 2015	Sep. 30, 2014
Equity, Class of Treasury Stock [Line Items]
Proceeds from issuance of preferred stock						$ 742	$ 742
Preferred stock cash dividend						$ 101	$ 43
Stock Repurchased During Period, Shares						15,600,000
Treasury Stock Acquired, Average Cost Per Share						$ 75.23
Stock Repurchased During Period, Value						$ 1,170
Cash dividends declared (in dollars per share)		$ 0.34		$ 0.3		$ 0.98	$ 0.86
Common stock dividends						$ (401)	$ (366)
Retained Earnings
Equity, Class of Treasury Stock [Line Items]
Preferred stock cash dividend						101	43
Common stock dividends		$ (138)		$ (126)		$ (401)	$ (366)
March 2015 Share Repurchase
Equity, Class of Treasury Stock [Line Items]
Amount of common stock authorized for repurchase			$ 1,800
Stock Repurchased During Period, Shares		4,800,000				9,300,000
Treasury Stock Acquired, Average Cost Per Share		$ 72.43				$ 75.47
Stock Repurchased During Period, Value		$ 350				$ 700
March 2014 Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Stock Repurchased During Period, Shares			6,300,000
Treasury Stock Acquired, Average Cost Per Share			$ 74.88
Stock Repurchased During Period, Value			$ 470
Stock Repurchase Program, Remaining Number of Shares Authorized to be Repurchased			0
Series F Preferred Stock, Depository Share
Equity, Class of Treasury Stock [Line Items]
Stock Issued During Period, Shares, New Issues	750,000
Preferred Stock, Liquidation Preference Per Share	$ 1,000
Preferred Stock, Dividends Per Share, Declared						$ 16.63
Ownership Interest in Preferred Stock	0.01
Series F Preferred Stock
Equity, Class of Treasury Stock [Line Items]
Preferred Stock, Liquidation Preference Per Share	$ 100,000
Proceeds from issuance of preferred stock	$ 742
Preferred Stock, Dividends Per Share, Declared					$ 0	$ 1,663
Preferred stock cash dividend						$ 12
Series E Preferred Stock, Depository Share
Equity, Class of Treasury Stock [Line Items]
Preferred Stock, Dividends Per Share, Declared		$ 0.38				$ 1.22
Series E Preferred Stock
Equity, Class of Treasury Stock [Line Items]
Preferred Stock, Dividends Per Share, Declared		$ 1,500				$ 4,833
Preferred stock cash dividend		$ 11				$ 36
Series D Preferred Stock, Depository Share
Equity, Class of Treasury Stock [Line Items]
Preferred Stock, Dividends Per Share, Declared		$ 0.37		$ 0.37		$ 1.11	$ 0.78
Series D Preferred Stock
Equity, Class of Treasury Stock [Line Items]
Preferred Stock, Dividends Per Share, Declared		$ 1,475		$ 1,475		$ 4,425	$ 3,130
Preferred stock cash dividend		$ 11		$ 11		$ 33	$ 23
Series C Preferred Stock, Depository Share
Equity, Class of Treasury Stock [Line Items]
Preferred Stock, Dividends Per Share, Declared		$ 0.33		$ 0.33		$ 0.99	$ 0.99
Series C Preferred Stock
Equity, Class of Treasury Stock [Line Items]
Preferred Stock, Dividends Per Share, Declared		$ 1,313		$ 1,313		$ 3,939	$ 3,939
Preferred stock cash dividend		$ 7		$ 7		$ 20	$ 20