Employee Incentive Plans, Weighted Average Grant Date Fair Value (Details) - $ / shares	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average grant-date fair value per share (in dollars per share)	$ 0.00	$ 0.00	$ 86.92	$ 86.11
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average grant-date fair value per share (in dollars per share)	82.33	0.00	76.13	75.57
TSR-Based Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average grant-date fair value per share (in dollars per share)	0.00	0.00	97.88	93.02
CP-Based Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average grant-date fair value per share (in dollars per share)	$ 0.00	$ 0.00	$ 79.69	$ 80.46