Income Taxes - Operating Loss Carryforwards and Tax Carryforwards (Details) $ in Millions	Dec. 31, 2015 USD ($)
Domestic Tax Authority [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	$ 2,817
State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	13,156
Valuation allowance on operating loss carryforwards	11,200
General Business Tax Credit Carryforward [Member] | State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Tax credit carryforwards	11
Valuation allowance on tax credit carryforward, Valuation Allowance	5
Tax Year 2033 [Member] | Domestic Tax Authority [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	1,741
Tax Year 2034 [Member] | Domestic Tax Authority [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	590
Tax Year 2035 [Member] | Domestic Tax Authority [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	486
Tax Years 2015 - 2020 [Member] | State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	320
Tax Years 2015 - 2019 [Member] | General Business Tax Credit Carryforward [Member] | State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Tax credit carryforwards	3
Tax Years 2021 - 2025 [Member] | State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	1,836
Tax Years 2026 - 2030 [Member] | State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	8,122
Tax Year 2031 [Member] | State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	2,878
No Expiration [Member] | General Business Tax Credit Carryforward [Member] | State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Tax credit carryforwards	$ 8