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Revenue from Contracts with Customers - Contract Balances (Details) - USD ($)
$ in Millions
Mar. 31, 2018
Jan. 01, 2018
Dec. 31, 2017
Revenue from Contract with Customer [Abstract]      
Accounts receivable, net $ 451 $ 534  
Contract assets 20 20  
Deferred revenue 532 395 $ 414
Long-term deferred revenue $ 72 $ 85 $ 85