Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	Sep. 30, 2021	Jun. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income	$ 3,534	$ 3,275	$ 2,834	$ 2,674	$ 2,479	$ 2,128
Foreign currency translation adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income	50		87
Net unrealized gains on investments, net of tax
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income	(2)		7
Accumulated other comprehensive income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income	$ 48	$ 70	$ 94	$ 52	$ 30	$ 25