Long-Term Debt - Summary of Maturity Dates, Semi-Annual Interest Payment Dates, and Optional Redemption Periods Of Outstanding Senior Note Obligations (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($)
Senior Notes due 2022 [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 1,600,000
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	Jan. 15, 2023	[1]
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	Mar. 01, 2024	[1]
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	Oct. 15, 2027	[1]
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	Dec. 01, 2043	[1]

[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 amounts specified in the respective senior note indentures plus any accrued and unpaid interest to the date of redemption. On or after the indicated dates, the Company may redeem all or a portion of its senior notes at a redemption amount equal to 100% of the principal amount of the senior notes being redeemed plus any accrued and unpaid interest to the date of redemption.