Stockholders' Equity - Schedule of Preferred Stock (Details) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($)
Class of Stock [Line Items]
Depository Share, Percent Interest in Preferred Stock	0.025
Preferred Stock, Including Additional Paid in Capital, Net of Discount	$ 4,360	$ 4,360
Series B Preferred Stock
Class of Stock [Line Items]
Preferred Stock, Dividend Rate, Percentage	6.00%
Redemption Price per Depositary Share (in dollars per share) | $ / shares	$ 1,000
Number of Depositary Shares (in shares) | shares	875,000
Preferred Stock, Including Additional Paid in Capital, Net of Discount	$ 853	853
Series C Preferred Stock
Class of Stock [Line Items]
Preferred Stock, Dividend Rate, Percentage	6.25%
Redemption Price per Depositary Share (in dollars per share) | $ / shares	$ 1,000
Number of Depositary Shares (in shares) | shares	500,000
Preferred Stock, Including Additional Paid in Capital, Net of Discount	$ 484	484
Series D Preferred Stock
Class of Stock [Line Items]
Preferred Stock, Dividend Rate, Percentage	6.70%
Redemption Price per Depositary Share (in dollars per share) | $ / shares	$ 1,000
Number of Depositary Shares (in shares) | shares	500,000
Preferred Stock, Including Additional Paid in Capital, Net of Discount	$ 485	485
Series E Preferred Stock
Class of Stock [Line Items]
Preferred Stock, Dividend Rate, Percentage	5.55%
Redemption Price per Depositary Share (in dollars per share) | $ / shares	$ 1,000
Number of Depositary Shares (in shares) | shares	1,000,000
Preferred Stock, Including Additional Paid in Capital, Net of Discount	$ 988	988
Preferred Stock, Dividend Payment Rate, Variable	Libor + 380 bps
Preferred Stock Dividend Rate, Variable	3.80%
Series F Preferred Stock
Class of Stock [Line Items]
Preferred Stock, Dividend Rate, Percentage	6.20%
Redemption Price per Depositary Share (in dollars per share) | $ / shares	$ 1,000
Number of Depositary Shares (in shares) | shares	500,000
Preferred Stock, Including Additional Paid in Capital, Net of Discount	$ 484	484
Series G Preferred Stock
Class of Stock [Line Items]
Preferred Stock, Dividend Rate, Percentage	5.20%
Redemption Price per Depositary Share (in dollars per share) | $ / shares	$ 1,000
Number of Depositary Shares (in shares) | shares	600,000
Preferred Stock, Including Additional Paid in Capital, Net of Discount	$ 583	583
Series H Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock, Dividend Rate, Percentage	6.00%
Redemption Price per Depositary Share (in dollars per share) | $ / shares	$ 1,000
Number of Depositary Shares (in shares) | shares	500,000
Preferred Stock, Including Additional Paid in Capital, Net of Discount	$ 483	$ 483