Annual report pursuant to Section 13 and 15(d)

Schedule I - Condensed Financial Information of Registrant - Balances per Condensed Balance Sheet (Details)

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Schedule I - Condensed Financial Information of Registrant - Balances per Condensed Balance Sheet (Details) - USD ($)
$ in Millions
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Condensed Cash Flow Statements, Captions [Line Items]        
Cash and cash equivalents $ 722 $ 876    
Non-current restricted cash 11 91    
Total cash, cash equivalents and restricted cash 2,613 1,827 $ 1,736 $ 2,780
Parent Company [Member]        
Condensed Cash Flow Statements, Captions [Line Items]        
Cash and cash equivalents 0 0    
Non-current restricted cash 0 7    
Total cash, cash equivalents and restricted cash $ 0 $ 7 $ 7 $ 6