Net Income Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Basic
Net income	$ 304.0	$ 502.2	$ 648.6	$ 409.6	$ 407.0	$ 705.8	$ 595.9	$ 321.7	$ 1,864.4	$ 2,030.4	$ 1,541.3
Average common shares outstanding (in shares)									262,500,000	271,300,000	275,400,000
Basic (in dollars per share)	$ 1.17	$ 1.92	$ 2.47	$ 1.54	$ 1.51	$ 2.60	$ 2.20	$ 1.18	$ 7.10	$ 7.48	$ 5.60
Diluted
Net income	$ 304.0	$ 502.2	$ 648.6	$ 409.6	$ 407.0	$ 705.8	$ 595.9	$ 321.7	$ 1,864.4	$ 2,030.4	$ 1,541.3
Average shares outstanding assuming dilution:
Average common shares outstanding (in shares)									262,500,000	271,300,000	275,400,000
Stock options and other contingently issuable shares (in shares)									4,600,000	4,500,000	4,800,000
Non-vested restricted stock grants (in shares)									0	0	100,000
Average common shares outstanding assuming dilution (in shares)									267,100,000	275,800,000	280,300,000
Diluted (in dollars per share)	$ 1.15	$ 1.88	$ 2.42	$ 1.51	$ 1.49	$ 2.55	$ 2.16	$ 1.15	$ 6.98	$ 7.36	$ 5.50
Net Income Per Common Share (Textual) [Abstract]
Anti-dilutive shares (in shares)									900,000	1,000,000	1,300,000