Financial Instruments Cross-currency forward-exchange contracts (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Foreign Currency Fair Value Hedge Derivative [Line Items]
Unrealized (losses)/gains on derivatives for net investment hedges, net	$ (8)	$ (14)	$ 17	$ 3
Derivatives Designated as Hedging Instruments: | Forward-starting interest rate swap contracts
Foreign Currency Fair Value Hedge Derivative [Line Items]
Unrealized (losses)/gains on derivatives for net investment hedges, net	(20)	0	19	(27)
Derivatives Designated as Hedging Instruments: | Cross-currency interest rate swap contracts
Foreign Currency Fair Value Hedge Derivative [Line Items]
Unrealized (losses)/gains on derivatives for net investment hedges, net	$ (8)	$ (14)	$ 17	$ 3