Stock-based Compensation - Unvested Shares Relating To Stock Options (Details) - Unvested Stock Options - $ / shares shares in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Shares
Beginning balance (in shares)	0.6	0.7
Granted (in shares)	0.0	0.3
Vested (in shares)	(0.1)	(0.2)
Forfeited (in shares)	0.0	(0.2)
Ending balance (in shares)	0.5	0.6
Weighted Average Grant Date Fair Value
Beginning of period weighted average grant date fair value (dollars per share)	$ 66.20	$ 67.95
Granted weighted average grant date fair value (dollars per share)	0	61.84
Vested weighted average grant date fair value (dollars per share)	66.66	66.72
Forfeited weighted average grant date fair value (dollars per share)	46.36	60.45
Ending of period weighted average grant date fair value (dollars per share)	$ 65.99	$ 66.20