Debt - Summary (Details) - USD ($) $ in Millions	3 Months Ended
	Sep. 30, 2020	Aug. 17, 2020	Dec. 31, 2019	Nov. 26, 2019	May 17, 2018	Sep. 22, 2016	Aug. 18, 2015	May 26, 2015
Debt Instrument [Line Items]
Long-term debt	$ 4,110		$ 3,948
Senior Notes | 4.0% Senior Notes due 2025
Debt Instrument [Line Items]
Stated interest rate (as a percent)	4.00%							4.00%
Long-term debt	$ 695		694
Unamortized debt discount and issuance costs	$ 5
Senior Notes | 4.4% Senior Notes, due 2026
Debt Instrument [Line Items]
Stated interest rate (as a percent)	4.40%						4.40%
Long-term debt	$ 0		893
Early repayment of debt	$ 900
Senior Notes | 2.95% Senior Notes due 2027
Debt Instrument [Line Items]
Stated interest rate (as a percent)	2.95%					2.95%
Long-term debt	$ 495		493
Unamortized debt discount and issuance costs	$ 5
Senior Notes | 2.5% Senior Notes due 2029
Debt Instrument [Line Items]
Stated interest rate (as a percent)	2.50%			2.50%
Long-term debt	$ 495		495
Unamortized debt discount and issuance costs	$ 5
Senior Notes | 1.25% Senior Notes due 2030
Debt Instrument [Line Items]
Stated interest rate (as a percent)	1.25%	1.25%
Long-term debt	$ 592		$ 0
Unamortized debt discount and issuance costs	$ 8
Senior Notes | 6.55% Senior Notes due 2037
Debt Instrument [Line Items]
Stated interest rate (as a percent)	6.55%		6.55%
Long-term debt	$ 290		$ 294
Unamortized debt discount and issuance costs	$ 3
Senior Notes | 4.5% Senior Notes due 2048
Debt Instrument [Line Items]
Stated interest rate (as a percent)	4.50%				4.50%
Long-term debt	$ 273		490
Unamortized debt discount and issuance costs	$ 10
Senior Notes | 3.25% Senior Notes due 2049
Debt Instrument [Line Items]
Stated interest rate (as a percent)	3.25%			3.25%
Long-term debt	$ 589		589
Unamortized debt discount and issuance costs	$ 11
Senior Notes | 2.3% Senior Notes due 2060
Debt Instrument [Line Items]
Stated interest rate (as a percent)	2.30%	2.30%
Long-term debt	$ 681		$ 0
Unamortized debt discount and issuance costs	$ 19