Stockholders' Equity - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	3 Months Ended			6 Months Ended
	May. 31, 2015	Jun. 30, 2015	Mar. 31, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Equity, Class of Treasury Stock [Line Items]
Proceeds from issuance of preferred stock					$ 742	$ 742
Preferred stock cash dividend					$ 60	$ 25
Stock Repurchased During Period, Shares		10,700,000
Treasury Stock Acquired, Average Cost Per Share		$ 76.50
Stock Repurchased During Period, Value		$ 820
Cash dividends declared (in dollars per share)		$ 0.34		$ 0.3	$ 0.64	$ 0.56
Common stock dividends					$ (262)	$ (240)
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		4,400,000
Treasury Stock Acquired, Average Cost Per Share		$ 78.79
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		$ 350	$ 470
Stock Repurchase Program, Remaining Number of Shares Authorized to be Repurchased			0
Series F Preferred Stock, Depository Share [Member]
Equity, Class of Treasury Stock [Line Items]
Stock Issued During Period, Shares, New Issues	750,000
Preferred Stock, Liquidation Preference Per Share	$ 1,000
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
Series C Preferred Stock
Equity, Class of Treasury Stock [Line Items]
Preferred Stock, Dividends Per Share, Declared		$ 1,313		$ 1,313	$ 2,626	$ 2,626
Preferred stock cash dividend		$ 7		$ 7	$ 13	$ 13
Series C Preferred Stock, Depository Share
Equity, Class of Treasury Stock [Line Items]
Preferred Stock, Dividends Per Share, Declared		$ 0.33		$ 0.33	$ 0.66	$ 0.66
Series D Preferred Stock
Equity, Class of Treasury Stock [Line Items]
Preferred Stock, Dividends Per Share, Declared		$ 1,475		$ 1,655	$ 2,950
Preferred stock cash dividend		$ 11		$ 12	$ 22
Series D Preferred Stock, Depository Share
Equity, Class of Treasury Stock [Line Items]
Preferred Stock, Dividends Per Share, Declared		$ 0.37		$ 0.41	$ 0.74
Series E Preferred Stock
Equity, Class of Treasury Stock [Line Items]
Preferred Stock, Dividends Per Share, Declared		$ 1,500			$ 3,333	$ 0
Preferred stock cash dividend		$ 11			$ 25
Series E Preferred Stock, Depository Share
Equity, Class of Treasury Stock [Line Items]
Preferred Stock, Dividends Per Share, Declared		$ 0.38			$ 0.84
Retained Earnings
Equity, Class of Treasury Stock [Line Items]
Preferred stock cash dividend					$ 60	$ 25
Common stock dividends		$ (139)		$ (128)	$ (262)	$ (240)