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Guarantee Of Registered Securities (Narrative) (Details)
12 Months Ended
Dec. 31, 2017
USD ($)
Guarantor Obligations [Line Items]  
Senior notes aggregate outstanding principal balance $ 1,000,000,000
8.50% Senior Notes Due 2019 [Member]  
Guarantor Obligations [Line Items]  
Senior Note Maturity Year 2019
Debt instrument interest rate stated percentage 8.50%
6.875% Senior notes due 2020  
Guarantor Obligations [Line Items]  
Senior Note Maturity Year 2020
Debt instrument interest rate stated percentage 6.875%
7.875% Senior Notes Due 2040 [Member]  
Guarantor Obligations [Line Items]  
Senior Note Maturity Year 2040
Debt instrument interest rate stated percentage 7.875%
7.20% Senior notes due 2027  
Guarantor Obligations [Line Items]  
Senior Note Maturity Year 2027
Debt instrument interest rate stated percentage 7.20%
Notes Issued $ 150,000,000