Income Taxes - Operating Loss Carryforward (Details) $ in Millions	3 Months Ended			12 Months Ended
	Dec. 31, 2016 USD ($)	Jun. 30, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Operating Loss Carryforwards [Line Items]
percentage change in a cumulative ownership shift				50
percent of stockholders				5.00%
Recognized Income Tax Benefit	$ 16	$ 0	$ 3,300
Deferred Income Tax Expense (Benefit)				$ (120)	$ 3,186	$ 117
Effective Income Tax Rate Reconciliation, Share-based Compensation, Excess Tax Benefit, Amount				22
Deferred Tax Assets, Valuation Allowance	862		1,002	862	1,002
U.S. Internal Revenue Service (IRS)
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	9,037			9,037
Recognized Income Tax Benefit	(110)		3,300
Deferred Income Tax Expense (Benefit)			3,100
Deferred Tax Assets, Valuation Allowance	900		$ 1,000	900	$ 1,000
U.S. Internal Revenue Service (IRS) | 2024
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	891			891
U.S. Internal Revenue Service (IRS) | 2025
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	1,267			1,267
U.S. Internal Revenue Service (IRS) | 2026
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	1,254			1,254
U.S. Internal Revenue Service (IRS) | 2027
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	1,645			1,645
U.S. Internal Revenue Service (IRS) | 2028
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	477			477
U.S. Internal Revenue Service (IRS) | 2029
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	694			694
U.S. Internal Revenue Service (IRS) | 2030
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	663			663
U.S. Internal Revenue Service (IRS) | 2031
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	833			833
U.S. Internal Revenue Service (IRS) | 2032
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	729			729
U.S. Internal Revenue Service (IRS) | 2033
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	194			194
U.S. Internal Revenue Service (IRS) | 2034
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	389			389
U.S. Internal Revenue Service (IRS) | 2035
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	1			1
Foreign jurisdiction
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforward, Disregarded for Domestic Country Tax Purposes	5,500			5,500
State jurisdiction
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	$ 9,400			$ 9,400