Income Taxes - Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits - Beginning of year	$ 145	$ 49	$ 42
Increases for assumed tax positions related to First Data	0	82	0
Increases for tax positions taken during the current year	9	8	3
Increases for tax positions taken in prior years	53	16	20
Decreases for tax positions taken in prior years	(23)	(2)	(8)
Decreases for settlements	(2)	(1)	0
Lapse of the statute of limitations	(11)	(7)	(8)
Unrecognized tax benefits - End of year	$ 171	$ 145	$ 49