XML 82 R66.htm IDEA: XBRL DOCUMENT v3.10.0.1
Summary of Significant Accounting Policies - Restricted Cash (Details) - USD ($)
$ in Millions
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Accounting Policies [Abstract]        
Cash and cash equivalents $ 563 $ 770 $ 591  
Funds deposited by counterparties 33 37 2  
Restricted cash 17 279 267  
Cash and cash equivalents, funds deposited by counterparties and restricted cash shown in the statements of cash flows $ 613 $ 1,086 $ 860 $ 1,042