Annual report pursuant to Section 13 and 15(d)

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

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Schedule I - Condensed Financial Information of Registrant - Balances per Condensed Balance Sheets (Details) - USD ($)
$ in Millions
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Balances per Consolidated Balance Sheets:        
Cash and cash equivalents $ 0 $ 0    
Restricted cash 1,589 605    
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents 1,589 605 $ 434 $ 989
Parent Company [Member]        
Balances per Consolidated Balance Sheets:        
Cash and cash equivalents 0 0    
Restricted cash 1,033 234    
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents $ 1,033 234 $ 110 $ 222
Total cash, cash equivalents and restricted cash   $ 234