Revenue from Contracts with Customers - Contract Assets Rollforward (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Capitalized Cost To Fulfill Customer Contracts
Change in Capitalized Contract Costs
Balance at beginning of period	$ 335	$ 329
Additions	1,360	1,453
Amortization	(1,360)	(1,447)
Impairment	0	0
Foreign currency translation and other	4	0
Balance at end of period	339	335
Capitalized Cost To Obtain Customer Contracts
Change in Capitalized Contract Costs
Balance at beginning of period	171	156
Additions	61	58
Amortization	(47)	(44)
Impairment	0	0
Foreign currency translation and other	(1)	1
Balance at end of period	$ 184	$ 171