Revisions of Previously Issued Financial Statements - Reconciliation of Cash, Cash Equivalents, and Restricted Cash (Details) - USD ($) $ in Millions	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents	$ 1,681	$ 1,214	$ 509	$ 388	$ 335	$ 414	$ 464
Restricted cash included in other assets	9	7	7	21	10	9	12
Funds held for clients included in other current assets	28	44	32	45	46	64	46
Cash included in settlement processing assets included in other current assets	21	8	15	9	10	9	10
Total cash, cash equivalents and restricted cash	$ 1,739	$ 1,273	$ 563	$ 463	$ 401	$ 496	$ 532