Shareholders' Equity - Schedule of Stock Repurchases (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended					4 Months Ended	9 Months Ended		102 Months Ended
	Sep. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Oct. 25, 2019	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020
Equity, Class of Treasury Stock [Line Items]
Total repurchase cost	$ 500.0	$ 463.0	$ 350.0	$ 1,056.0	$ 101.0
2012 - Share Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Shares purchased (in shares)	2,400		1,800			25	4,600	8,200	133,400
Average price per share (in dollars per share)	$ 201.96		$ 190.83			$ 193.91	$ 207.01	$ 183.26
Total repurchase cost	$ 500.0		$ 350.0			$ 4.8	$ 961.0	$ 1,500.0	$ 13,900.0
Additional associated costs	0.0		0.0				2.0	7.0
Total costs recorded to retained earnings	$ 500.0		$ 350.0				$ 963.0	$ 1,507.0