Income Taxes Income Taxes - Effective Income Tax Rate Reconciliation (Details) - USD ($)	1 Months Ended	2 Months Ended	3 Months Ended	5 Months Ended	6 Months Ended
	Jun. 30, 2018	May 31, 2018	Jun. 30, 2017	May 31, 2018	Jun. 30, 2017
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount	$ 15,000,000	$ (9,000,000)	$ 51,000,000	$ 21,000,000	$ 81,000,000
Effective Income Tax Rate Reconciliation, Deduction, Dividends, Amount	0	(5,000,000)	(18,000,000)	(12,000,000)	(36,000,000)
Income Tax Reconciliation, Deductions, Foreign Investments	(1,000,000)	(1,000,000)	(2,000,000)	(3,000,000)	(3,000,000)
Tax Cuts and Jobs Act of 2017, Deferred Tax Asset, Income Tax Expense (Benefit)	0	0	0	(2,000,000)	0
Effective Income Tax Rate Reconciliation, Other Adjustments, Amount	0	(3,000,000)	(2,000,000)	(3,000,000)	(2,000,000)
Income Tax Expense (Benefit)	$ 14,000,000	$ (12,000,000)	$ 33,000,000	$ 7,000,000	$ 44,000,000