Consolidating Financial Information - Narrative (Details) - Senior Notes	Mar. 31, 2018 USD ($)
8.75% due 2020
Debt Instrument [Line Items]
Debt instrument, face amount	$ 282,000,000
Interest rate, stated percentage	8.75%
5.125% due 2023
Debt Instrument [Line Items]
Debt instrument, face amount	$ 1,000,000,000
Interest rate, stated percentage	5.125%
5% due 2026
Debt Instrument [Line Items]
Debt instrument, face amount	$ 900,000,000
Interest rate, stated percentage	5.00%
4.875% due 2027
Debt Instrument [Line Items]
Debt instrument, face amount	$ 700,000,000
Interest rate, stated percentage	4.875%