Stock-Based Compensation Plans - Activity for Awards Made Outside of Share-Based Compensation Plans (Details) - $ / shares shares in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Restricted stock
Number of Shares/Units
Shares, granted (in shares)	29	35	137
ELTI Plan, the 2013 New Company LTIP, the 2007 Incentive Plan and awards made outside of stock-based compensation plans
Number of Shares/Units
Shares outstanding, beginning of period (in shares)	197	285	349
Shares, granted (in shares)	79	83	183
Shares, adjustments (in shares)	15
Shares, vested (in shares)	(143)	(167)	(242)
Shares cancelled/forfeited (in shares)	(1)	(4)	(5)
Shares outstanding, end of period (in shares)	147	197	285
Weighted Average Grant Date Fair Value
Shares outstanding, weighted average grant date fair value, beginning of period (in dollars per share)	$ 111.69	$ 83.71	$ 56.40
Shares, weighted average grant date fair value, granted (in dollars per share)	159.75	135.71	107.06
Shares, weighted average grant date fair value, adjustments (in dollars per share)	153.01
Shares, weighted average grant date fair value, vested (in dollars per share)	119.94	67.61	57.24
Shares, weighted average grant date fair value, cancelled/forfeited (in dollars per share)	125.75	88.92	91.14
Shares outstanding, weighted average grant date fair value, end of period (in dollars per share)	$ 130.75	$ 111.69	$ 83.71
Market Condition & Performance-Based Awards | ELTI Plan, the 2013 New Company LTIP, the 2007 Incentive Plan and awards made outside of stock-based compensation plans
Number of Shares/Units
Shares outstanding, beginning of period (in shares)	37	17	85
Shares, granted (in shares)	21	20	17
Shares, adjustments (in shares)	15
Shares, vested (in shares)	(32)	0	(85)
Shares cancelled/forfeited (in shares)	0	0	0
Shares outstanding, end of period (in shares)	41	37	17
Weighted Average Grant Date Fair Value
Shares outstanding, weighted average grant date fair value, beginning of period (in dollars per share)	$ 146.57	$ 153.01	$ 54.32
Shares, weighted average grant date fair value, granted (in dollars per share)	167.25	141.02	153.01
Shares, weighted average grant date fair value, adjustments (in dollars per share)	153.01
Shares, weighted average grant date fair value, vested (in dollars per share)	153.01	0.00	48.31
Shares, weighted average grant date fair value, cancelled/forfeited (in dollars per share)	0.00	0.00	0.00
Shares outstanding, weighted average grant date fair value, end of period (in dollars per share)	$ 154.78	$ 146.57	$ 153.01
Service Period Awards | ELTI Plan, the 2013 New Company LTIP, the 2007 Incentive Plan and awards made outside of stock-based compensation plans
Number of Shares/Units
Shares outstanding, beginning of period (in shares)	160	268	264
Shares, granted (in shares)	58	63	166
Shares, adjustments (in shares)	0
Shares, vested (in shares)	(111)	(167)	(157)
Shares cancelled/forfeited (in shares)	(1)	(4)	(5)
Shares outstanding, end of period (in shares)	106	160	268
Weighted Average Grant Date Fair Value
Shares outstanding, weighted average grant date fair value, beginning of period (in dollars per share)	$ 110.71	$ 71.98	$ 57.07
Shares, weighted average grant date fair value, granted (in dollars per share)	156.92	134.04	102.34
Shares, weighted average grant date fair value, adjustments (in dollars per share)	0.00
Shares, weighted average grant date fair value, vested (in dollars per share)	110.38	67.61	65.89
Shares, weighted average grant date fair value, cancelled/forfeited (in dollars per share)	125.75	88.92	91.14
Shares outstanding, weighted average grant date fair value, end of period (in dollars per share)	$ 136.54	$ 110.71	$ 71.98