Stockholders' Equity (Preferred Stock Issued and Outstanding) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	Dec. 31, 2016	Oct. 31, 2016	Mar. 07, 2016	Dec. 31, 2015		Aug. 03, 2015
Class of Stock [Line Items]
Shares Issued and Outstanding	2,241			1,485
Liquidation Preference	$ 2,835			$ 1,485
Carrying Value	$ 2,783			$ 1,459	[1]
Series A Preferred Stock [Member]
Class of Stock [Line Items]
Shares Issued and Outstanding	400			400
Preferred stock liquidation preference (per share)	$ 1,000			$ 1,000
Liquidation Preference	$ 400			$ 400
Carrying Value	$ 397			$ 396
Series B Preferred Stock [Member]
Class of Stock [Line Items]
Shares Issued and Outstanding	485			485
Preferred stock liquidation preference (per share)	$ 1,000			$ 1,000
Liquidation Preference	$ 485			$ 485
Carrying Value	$ 482			$ 480
Series C Preferred Stock [Member]
Class of Stock [Line Items]
Shares Issued and Outstanding	600			600
Preferred stock liquidation preference (per share)	$ 1,000			$ 1,000		$ 1,000
Liquidation Preference	$ 600			$ 600
Carrying Value	$ 585			$ 583
Series D Preferred Stock [Member]
Class of Stock [Line Items]
Shares Issued and Outstanding	750
Preferred stock liquidation preference (per share)	$ 1,000		$ 1,000
Liquidation Preference	$ 750
Carrying Value	$ 728
Series E Preferred Stock [Member]
Class of Stock [Line Items]
Shares Issued and Outstanding	6
Preferred stock liquidation preference (per share)	$ 100,000	$ 100,000
Liquidation Preference	$ 600
Carrying Value	$ 591

[1] Adjusted for the retrospective adoption of ASU 2015-03. See New Accounting Standards in Note 2 for additional information.