Summary of Significant Accounting Policies - Settlement Assets and Obligations (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Accounting Policies [Abstract]
Settlement assets	$ 486	$ 385
Settlement obligations	$ 480	$ 379

Cash received or short term receivables for unsettled money transfers, money orders, consumer payments, or business to business payments. Settlement assets include clearing and settling customers payments due to and from financial institutions and may include cash and cash equivalents.

No definition available.

Name:	us-gaap_SettlementAssetsCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant