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Stock Compensation Plans Stock Options (Narrative) (Details)
shares in Thousands, $ in Millions
12 Months Ended
Mar. 31, 2011
shares
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
shares
Dec. 31, 2015
USD ($)
shares
Dec. 31, 2014
USD ($)
shares
Mar. 30, 2011
USD ($)
shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Vesting period   3 years        
Stock Options            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Incentive stock plan conversion factor determined in spin-off agreement           1.65
Stock options, Outstanding     262 533 644  
Stock options, Outstanding, Intrinsic Value | $     $ 38 $ 50 $ 49  
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value | $   $ 43 $ 26 $ 11    
Stock Options | 2011 Long Term Incentive Stock Plan [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Stock options issued, number after conversion 1,600          
Options fully vested at time of conversion, number           1,400
Stock options, Outstanding, Intrinsic Value | $           $ 15
Stock Options | Granted Prior to 2008 [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Stock options, Outstanding           1,000
Vesting rate   .25        
Vesting period   4 years        
Number of years until expiration   10 years        
Stock Options | Granted after 2008 [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Vesting rate   .33        
Vesting period   3 years        
Number of years until expiration   7 years