Long-Term Debt Long-Term Debt - Summary of Maturity Dates, Semi-Annual Interest Payment Dates, and Optional Redemption Periods of Outstanding Senior Note Obligations (Details)	3 Months Ended
	Mar. 31, 2015
2020 Notes [Member]
Debt Instrument [Line Items]
Maturity date	Oct. 01, 2020
Interest payment dates	April 1, Oct. 1
Call premium redemption period	Oct. 01, 2015
Make-whole redemption period	Oct. 01, 2015
2021 Notes [Member]
Debt Instrument [Line Items]
Maturity date	Apr. 01, 2021
Interest payment dates	April 1, Oct. 1
Call premium redemption period	Apr. 01, 2016
Make-whole redemption period	Apr. 01, 2016
2022 Notes [Member]
Debt Instrument [Line Items]
Maturity date	Sep. 15, 2022
Interest payment dates	March 15, Sept. 15
Call premium redemption period	Mar. 15, 2017
Make-whole redemption period	Mar. 15, 2017
2023 Notes [Member]
Debt Instrument [Line Items]
Maturity date	Apr. 15, 2023
Interest payment dates	April 15, Oct. 15
Make-whole redemption period	Jan. 15, 2023
Senior Notes due 2024 [Domain]
Debt Instrument [Line Items]
Maturity date	Jun. 01, 2024
Interest payment dates	June 1, Dec. 1
Make-whole redemption period	Mar. 01, 2024
Senior Notes due 2044 [Member]
Debt Instrument [Line Items]
Maturity date	Jun. 01, 2044
Interest payment dates	June 1, Dec. 1
Make-whole redemption period	Dec. 01, 2043