Summary of Significant Accounting Policies - Reclassifications (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Cash and cash equivalents	$ 385	$ 429	$ 358	$ 425
Restatement adjustment prior years
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Cash and cash equivalents	102
Net cash provided by operating activities	$ 102