Income Taxes - Additional Information (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Taxes Other Information [Line Items]
Unrecognized Tax Benefits that Would Impact Effective Tax Rate		$ 74
Deferred Tax Assets, Valuation Allowance		$ 80	$ 79
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent		35.00%	35.00%	35.00%
Unrecognized Tax Benefits, Interest on Income Taxes Accrued		$ 8	$ 8
Unrecognized Tax Benefits, Interest on Income Taxes Expense		1	4
Decrease in Unrecognized Tax Benefits is Reasonably Possible		5
Effective Income Tax Rate Reconciliation, Tax Credit, Amount	[1]	(86)	(69)	$ (65)
Investments [Member]
Income Taxes Other Information [Line Items]
Effective Income Tax Rate Reconciliation, Tax Credit, Amount		$ (2)	$ (6)	$ (21)
Minimum [Member]
Income Taxes Other Information [Line Items]
Operating Loss Carryforwards, Limitations on Use		2017
Maximum [Member]
Income Taxes Other Information [Line Items]
Operating Loss Carryforwards, Limitations on Use		2036

[1] Excludes income tax benefits of $2 million, $6 million, and $21 million for the years ended December 31, 2016, 2015, and 2014, respectively, related to tax credits, which were recognized as a reduction to the related investment asset.