Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Net income (loss)	$ 459.5	$ 314.8	$ 862.0	$ 668.4
Subtract:
Net income (loss) attributable to noncontrolling interest	2.9	5.3	8.3	10.0
Total	$ 456.6	$ 309.5	$ 853.7	$ 658.4
Weighted-average shares outstanding:
Basic	286.4	288.9	287.9	288.6
Dilutive effects:
Diluted	289.2	292.7	291.1	292.5
Net income (loss) per common share:
Basic	$ 1.59	$ 1.07	$ 2.97	$ 2.28
Diluted	$ 1.58	$ 1.06	$ 2.93	$ 2.25
Nonqualified Stock Options
Dilutive effects:
Stock-based compensation awards	1.0	1.8	1.2	1.8
Restricted Stock Units
Dilutive effects:
Stock-based compensation awards	1.6	1.8	1.8	1.9
Performance Share Awards
Dilutive effects:
Stock-based compensation awards	0.2	0.2	0.2	0.2