Income Taxes - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Tax Legislation expense (benefit)	$ (506,000,000)
Effective income tax rate (as a percent)	20.10%	31.90%	33.90%
Tax Legislation benefit	(12.70%)	0.00%	0.00%
Income tax penalties and interest expense	$ 0	$ 0	$ 0
Interest on income taxes accrued	0	0
Net operating loss carryforward	238,000,000
Income tax paid	968,000,000	359,000,000	$ 1,070,000,000
Current income tax payable	$ 44,000,000	135,000,000
Unrecognized tax benefits, income tax penalties accrued		$ 0