Contingencies - Narrative (Details) £ in Millions		1 Months Ended
	Jan. 18, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jan. 31, 2014 USD ($)	Jan. 31, 2014 GBP (£)	Dec. 31, 2016 USD ($)
Loss Contingencies [Line Items]
Unrecognized tax benefits		$ 63,000,000			$ 71,000,000
Minimum
Loss Contingencies [Line Items]
Estimate of possible loss		0
Maximum
Loss Contingencies [Line Items]
Estimate of possible loss		15,000,000
Legal Reserve | Invoicing Matter
Loss Contingencies [Line Items]
Estimate of possible loss		340,000,000
U.K. FCA | Regulatory Matter | Transition Management
Loss Contingencies [Line Items]
Settlement, amount			$ 37,800,000	£ 22.9
Department of Justice | Regulatory Matter | Transition Management
Loss Contingencies [Line Items]
Settlement, amount	$ 32,300,000
SEC | Regulatory Matter | Transition Management
Loss Contingencies [Line Items]
Settlement, amount		$ 32,300,000