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Commitments and Contingencies - Expenses and Insurance Recoveries (Details) £ in Millions, $ in Millions	1 Months Ended	3 Months Ended	6 Months Ended
	Mar. 15, 2019 lawsuit	Jun. 30, 2019 USD ($) lawsuit	Jun. 30, 2019 USD ($) lawsuit	Jun. 30, 2019 GBP (£) lawsuit
Data Security Incident
Loss Contingencies [Line Items]
Expense related to data security incident		$ 148	$ 192
Insurance recoveries related to data security incident		22	68
Data Security Incident, UK Information Commissioner's Office
Loss Contingencies [Line Items]
Estimated fine \| £				£ 99
Accrual for loss contingency		$ 126	$ 126
Putative Class Action Lawsuits Related to Data Security Incident
Loss Contingencies [Line Items]
Number of lawsuits filed \| lawsuit		100	100	100
Shareholder Derivative Complaints Related to Data Security Incident
Loss Contingencies [Line Items]
Number of new lawsuits filed \| lawsuit	2