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Stock-Based Compensation and Earnings Per Share - Assumptions Used to Value Option Grants (Details) - USD ($)
shares in Millions, $ in Millions
3 Months Ended 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Sep. 30, 2017
Options Assumptions [Line Items]      
Risk free interest rate, minimum     1.00%
Risk free interest rate, maximum     2.70%
Expected volatility     19.00%
Expected life     7 years
Common stock issued to employees under employee stock purchase and defined contribution savings plans (in shares) 0.1   0.2
Compensation and benefits paid in common stock $ 13 $ 16 $ 16
Minimum      
Options Assumptions [Line Items]      
Expected dividend yield     1.30%
Maximum      
Options Assumptions [Line Items]      
Expected dividend yield     1.50%