Income Taxes - Differences Between Provisions for Income Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Valuation Allowance [Line Items]
Transition tax for accumulated foreign earnings	$ 9
Sequestration of AMT credits	3
Change in tax rate, provisional income tax expense (benefit)	9
Differences between actual provisions for income taxes and provisions for income taxes at the U.S. federal statutory rate (35%)
Taxes on income from continuing operations at U.S. federal statutory rate	117	$ 96	$ 82
Foreign earnings subject to different tax rates	3	(3)	(3)
State income tax, net of federal benefit	9	10	8
Change in valuation allowance	0	0	(827)
Income from equity method investments	(21)	(17)	(16)
Law changes	145	0	0
Prior year return adjustments	(7)	0	0
Benefits from unrecognized tax positions	0	0	(6)
Foreign tax credits	0	(21)	0
Tax expense on distribution of foreign earnings	0	0	20
Other, net	(8)	(2)	2
Provision for income tax expense (benefit)	$ 238	$ 63	$ (740)
Effective income tax rate	71.00%	22.90%	(313.60%)
Foreign Tax Credits
Valuation Allowance [Line Items]
Change in tax rate, deferred tax asset, valuation allowance	$ 106
State Net Operating Losses
Valuation Allowance [Line Items]
Change in tax rate, deferred tax asset, valuation allowance	$ 18