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Debt and lines of credit - Additional Information (Details) - USD ($)	1 Months Ended	3 Months Ended			9 Months Ended
	Aug. 31, 2019	Sep. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Debt Instrument [Line Items]
Commercial paper		$ 0			$ 0
Proceeds from issuance of long-term debt					1,491,000,000	$ 1,500,000,000
Interest and debt expense		43,000,000		$ 36,000,000	125,000,000	$ 89,000,000
Notes due 2019 at 1.65%
Debt Instrument [Line Items]
Retirement of debt	$ 750,000,000
Notes due 2039 at 3.875%
Debt Instrument [Line Items]
Principal amount			$ 750,000,000
Payments of debt issuance costs			7,000,000
Proceeds from issuance of long-term debt			$ 743,000,000
Notes due 2029 at 2.25%
Debt Instrument [Line Items]
Principal amount		750,000,000			750,000,000
Payments of debt issuance costs		5,000,000
Proceeds from issuance of long-term debt		748,000,000
Revolving credit facility
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity		$ 2,000,000,000			$ 2,000,000,000