Fair Value Measurements - Estimated Fair Value (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets at fair value	$ 17	$ 21
Disputed claims liability	50	45
Total liabilities at fair value	893	391
Government bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Government bonds	17	15
Derivative instruments - interest rate swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments - interest rate swaps		6
Derivative instruments	85	22
Derivative instruments - CEC Convertible Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments	758	324
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets at fair value	0	0
Disputed claims liability	0	0
Total liabilities at fair value	0	0
Level 1 | Government bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Government bonds	0	0
Level 1 | Derivative instruments - interest rate swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments - interest rate swaps		0
Derivative instruments	0	0
Level 1 | Derivative instruments - CEC Convertible Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments	0	0
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets at fair value	17	21
Disputed claims liability	50	45
Total liabilities at fair value	893	391
Level 2 | Government bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Government bonds	17	15
Level 2 | Derivative instruments - interest rate swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments - interest rate swaps		6
Derivative instruments	85	22
Level 2 | Derivative instruments - CEC Convertible Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments	758	324
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets at fair value	0	0
Disputed claims liability	0	0
Total liabilities at fair value	0	0
Level 3 | Government bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Government bonds	0	0
Level 3 | Derivative instruments - interest rate swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments - interest rate swaps		0
Derivative instruments	0	0
Level 3 | Derivative instruments - CEC Convertible Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments	$ 0	$ 0