Long-Term Debt - Summary of Maturity Dates, Semi-Annual Interest Payment Dates, and Optional Redemption Periods Of Outstanding Senior Note Obligations (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Nov. 10, 2016
2021 Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount			$ 400,000
Senior Notes due 2022 [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount		$ 2,000,000
Maturity date		Sep. 15, 2022
Interest Payment Dates		March 15,  Sep 15
Senior Notes Due 2023 [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount		$ 1,500,000
Maturity date		Apr. 15, 2023
Interest Payment Dates		April 15, Oct 15
Make-whole redemption period	[1]	Jan. 15, 2023
Senior Notes due 2024 [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount		$ 1,000,000
Maturity date		Jun. 01, 2024
Interest Payment Dates		June 1, Dec 1
Make-whole redemption period	[1]	Mar. 01, 2024
Senior Notes due 2028 [Domain]
Debt Instrument [Line Items]
Debt Instrument, Face Amount		$ 1,000,000
Maturity date		Jan. 15, 2028
Interest Payment Dates		Jan 15, July 15
Make-whole redemption period	[1]	Oct. 15, 2027
2020 Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount			$ 200,000
Senior Notes due 2044 [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount		$ 700,000
Maturity date		Jun. 01, 2044
Interest Payment Dates		June 1, Dec 1
Make-whole redemption period	[1]	Dec. 01, 2043

[1] At any time prior to the indicated dates, the Company has the option to redeem all or a portion of its senior notes of the applicable series at the “make-whole” redemption prices or amounts specified in the respective senior note indentures plus any accrued and unpaid interest to the date of redemption. On or after these dates, the Company may redeem all or a portion of its senior notes at a redemption price equal to 100% of the principal amount of the senior notes being redeemed plus any accrued and unpaid interest to the date of redemption.