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Employee Stock-based Compensation Plans Total Intrinsic Value of Options Exercised and The Cash Received (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]      
Intrinsic value of options exercised $ 6 $ 13 $ 8
Cash received from option exercises 19 18 9
Tax benefit realized from option exercises $ 2 $ 5 $ 3