Contract revenue - Narrative (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Capitalized Contract Cost [Line Items]
Contract with customer, asset	$ 2,500			$ 2,500		$ 2,400
Contract assets representing accrued revenues not yet billed	108			108		32
Contract with customer, liability	185			185		167
Contract with customer, liability, revenue recognized	68			101
Incremental costs for obtaining contracts
Capitalized Contract Cost [Line Items]
Capitalized contract costs	$ 62			$ 62		73
Capitalized contract cost, amortization period	9 years			9 years
Capitalized contract cost, amortization	$ 5	$ 5	$ 6	$ 15	$ 16
Costs to fulfill contract
Capitalized Contract Cost [Line Items]
Capitalized contract costs	19			19		$ 15
Capitalized contract cost, amortization	$ 1	$ 1	$ 1	$ 1	$ 4
Costs to fulfill contract | Minimum
Capitalized Contract Cost [Line Items]
Capitalized contract cost, amortization period	7 years			7 years
Costs to fulfill contract | Maximum
Capitalized Contract Cost [Line Items]
Capitalized contract cost, amortization period	9 years			9 years