Share-Based Compensation - Performance-Based and Restricted Stock Awards (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
PX Performance Based Awards
Additional Company Information [Abstract]
Vesting period	3 years
Number of Shares (000’s)
Non-vested at beginning of period (in shares)	665,000
Granted (in shares)	0
Vested (in shares)	(79,000)
Award conversions (in shares)	(435,000)
Cancelled and forfeited (in shares)	(151,000)
Non-vested at end of period (in shares)	0	665,000
Average Grant Date Fair Value
Non-vested at beginning of period (in dollars per share)	$ 113.40
Granted (in dollars per share)	0.00
Vested (in dollars per share)	119.98
Award conversions (in dollars per share)	0.00
Cancelled and forfeited (in dollars per share)	110.29
Non-vested at end of period (in dollars per share)	$ 0.00	$ 113.40
Restricted Stock
Additional Company Information [Abstract]
Awards to be settled in cash (in shares)	12,000
Unrecognized compensation expense	$ 30
Number of Shares (000’s)
Non-vested at beginning of period (in shares)	264,000
Granted (in shares)	278,907
Vested (in shares)	(153,000)
Award conversions (in shares)	704,000
Cancelled and forfeited (in shares)	(23,000)
Non-vested at end of period (in shares)	1,071,000	264,000
Average Grant Date Fair Value
Non-vested at beginning of period (in dollars per share)	$ 107.56
Granted (in dollars per share)	144.86	$ 111.95	$ 98.18
Vested (in dollars per share)	117.67
Award conversions (in dollars per share)	0.00
Cancelled and forfeited (in dollars per share)	111.41
Non-vested at end of period (in dollars per share)	$ 118.84	107.56
Performance Shares TSR
Average Grant Date Fair Value
Granted (in dollars per share)		124.12	124.18
Performance Shares ROC
Average Grant Date Fair Value
Granted (in dollars per share)		$ 109.68	$ 93.46