Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Net income (loss)	$ 491.5	$ 235.9	$ 416.1	$ 285.0	$ 315.3	$ 284.6	$ 392.1	$ 452.1	$ 1,428.5	$ 1,444.1	$ 1,553.7
Subtract:
Net income (loss) attributable to noncontrolling interest									32.7	49.9	7.2
Total									$ 1,395.8	$ 1,394.2	$ 1,546.5
Weighted-average shares outstanding:
Basic									274.7	278.6	285.8
Dilutive effects:
Diluted									276.6	281.0	288.8
Net income (loss) per common share:
Basic	$ 1.72	$ 0.86	$ 1.45	$ 1.05	$ 1.08	$ 0.99	$ 1.38	$ 1.54	$ 5.08	$ 5.00	$ 5.41
Diluted	$ 1.70	$ 0.85	$ 1.45	$ 1.04	$ 1.07	$ 0.98	$ 1.37	$ 1.53	$ 5.05	$ 4.96	$ 5.36
Nonqualified Stock Options
Dilutive effects:
Stock-based compensation awards									0.3	0.9	1.0
Restricted Stock Units
Dilutive effects:
Stock-based compensation awards									1.5	1.4	1.7
Performance Share Awards
Dilutive effects:
Stock-based compensation awards									0.1	0.1	0.3