XML 154 R128.htm IDEA: XBRL DOCUMENT v3.8.0.1
Incentive Plans (Narrative) (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Stock rights and stock units 5,799,884 5,950,130 5,857,733 7,275,934
Compensation cost related to unvested restricted performace shares, executive continuity awards and restricted stock attributable to future performance, net of estimated forfeitures $ 86      
Compensation cost related to unvested restricted performace shares, executive continuity awards and restricted stock attributable to future performance, net of estimated forfeitures, weighted-average period (in years) 1 year 9 months 1 day      
Stock Compensation Plan [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Shares available for grant 13,200,000 14,300,000 16,200,000  
Restricted performance share plan | Other Participants [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Weight of return on investment (ROI) on awards 75.00%      
Weight of total shareholder return (TSR) on awards 25.00%      
Restricted performance share plan | Officer [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Weight of return on investment (ROI) on awards 50.00%      
Weight of total shareholder return (TSR) on awards 50.00%