Investments and Cash Investments and Cash - Cash and Restricted Cash (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Cash	$ 72	$ 118	$ 98	$ 166
Restricted cash	0	9	1	0
Cash and Restricted Cash	$ 72	$ 127	$ 99	$ 166