Debt - Credit Facility (Details)	12 Months Ended
	Dec. 31, 2020 USD ($)	Jul. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Jul. 31, 2019 USD ($)
Line of Credit Facility [Line Items]
Line of credit facility, fair value of amount outstanding	$ 0		$ 0
Letters of credit	0		$ 0
Revolving Credit Facility
Line of Credit Facility [Line Items]
Line of credit facility, accordion feature	$ 750,000,000
Extension period	1 year
Debt guaranteed by domestic subsidiary	$ 100,000,000
Line of credit facility, commitment fee (percent)	0.25%
Revolving Credit Facility | Minimum
Line of Credit Facility [Line Items]
Line of credit facility, interest rate, base rate (percent)	0.00%
Line of credit facility, interest rate, LIBOR plus all-in spread rate	1.00%
All-in interest rate spread based on credit rating (percent)	0.375%
Line of credit facility, commitment fee (percent)	0.125%
Line of credit facility, covenant terms	3.00x
Revolving Credit Facility | Maximum
Line of Credit Facility [Line Items]
Line of credit facility, interest rate, base rate (percent)	0.70%
Line of credit facility, interest rate, LIBOR plus all-in spread rate	1.70%
All-in interest rate spread based on credit rating (percent)	1.375%
Line of credit facility, commitment fee (percent)	0.30%
Line of credit facility, covenant terms	4.25x
Current Credit Facility | Revolving Credit Facility
Line of Credit Facility [Line Items]
Line of credit facility, current borrowing capacity	$ 1,800,000,000
Letter of credit, credit facility sub-facility, maximum borrowing amount	$ 250,000,000
Credit Agreement Amendment No3
Line of Credit Facility [Line Items]
Minimum unrestricted cash		$ 1,000,000,000.0
Borrowed money to consolidated EBITDA		4.25
Cap on cash netting				$ 1,750,000,000