Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Effective Income Tax Rate Reconciliation [Line Items]
Valuation allowance	$ (78,000,000)	$ (44,000,000)
Deferred taxes, net	0	101,000,000
Impact of federal tax reform	30,000,000	0	$ 0
Changes in valuation allowance	(13,000,000)	5,000,000	10,000,000
Impact to effective income tax rate from nondeductible expenses related to legal and regulatory matters	3,000,000	6,000,000
Impact to effective income tax rate from nondeductible expenses related to employee share based payment, stock buyback expense, meals and entertainment expenses	4,000,000
Estimated liability for potential payment of interest and penalties	2,000,000	2,000,000
Impact of resolution of income tax contingencies or reductions in valuation allowances on effective income tax rate	11,000,000	8,000,000	$ 11,000,000
State
Effective Income Tax Rate Reconciliation [Line Items]
Changes in valuation allowance	$ (6,000,000)	$ 4,000,000