Debt - Narrative (Details) - USD ($)	Sep. 10, 2018	Sep. 30, 2018
Debt Instrument [Line Items]
Description of interest accrual date	Interest accrues on both the 2028 senior notes and 2048 senior notes from September 10, 2018 and will be paid in cash on March 15 and September 15 of each year, commencing on March 15, 2019.
Proceeds from Debt, Net of Issuance Costs	$ 989,000,000
Term loan due 2019 [Member]
Debt Instrument [Line Items]
Prepayment of outstanding debt	127,000,000
4.500% senior notes due 2028 [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 600,000,000
Stated interest rate	4.50%	4.50%
Effective interest rate (as a percent)	4.504%
Maturity date	Sep. 15, 2028
5.050% senior notes due 2048 [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 400,000,000
Stated interest rate	5.05%	5.05%
Effective interest rate (as a percent)	5.073%
Maturity date	Sep. 15, 2048
Revolving $1.25 billion credit facility [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 1,250,000,000