Debt - 5.000% Senior Unsecured Notes Due 2027 - Additional Information (Detail) - 5.000% Senior Unsecured Notes Due 2027 [Member] - USD ($)		12 Months Ended
	Sep. 07, 2017	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Senior unsecured notes face amount	$ 1,400,000,000
Senior unsecured notes, payable term		Interest on the notes is payable on April 15 and October 15 of each year
Senior unsecured notes, interest rate	5.00%	5.00%	5.00%
Senior unsecured notes, maturity date	Oct. 15, 2027
Senior notes, earliest redemption date	Oct. 15, 2022
Senior unsecured notes, redemption description		we may redeem up to 40% of the notes at a redemption price equal to 105% of the aggregate principal amount thereof, plus accrued and unpaid interest thereon, using proceeds from one or more equity offerings. In the event of a change in control, each holder of the notes may require us to repurchase some or all of the notes at a repurchase price equal to 101% of the aggregate principal amount of the notes plus accrued and unpaid interest to the date of purchase.
Debt instrument, redemption price percentage	105.00%
Senior notes, repurchased price percentage on principal amount plus accrued and unpaid interest	101.00%
Maximum [Member]
Debt Instrument [Line Items]
Senior unsecured notes, redemption percentage on principal amount	40.00%