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Equity Equity (Stock Repurchases) (Details) - USD ($)
$ / shares in Units, $ in Millions
 12 Months Ended 90 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2017
Equity, Class of Treasury Stock [Line Items]        
Stock Repurchase Program, Remaining Authorized Repurchase Amount $ 246     $ 246
Treasury Stock, Shares 155,924,785 156,878,891   155,924,785
Acquisition of treasury stock (shares) 0     154,300,000
Payments for Repurchase of Common Stock $ 0 $ 79 $ 482  
Treasury Stock Acquired, Average Cost Per Share       $ 12.12
Treasury Stock, Value, Acquired, Cost Method       $ 1,900