Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Net income (loss)	$ 813.2	$ 327.4	$ 1,481.6	$ 1,023.6
Subtract:
Net income (loss) attributable to noncontrolling interest	3.0	19.2	13.0	25.1
Total	$ 810.2	$ 308.2	$ 1,468.6	$ 998.5
Weighted-average shares outstanding
Basic	289.3	288.1	288.8	289.8
Dilutive effects:
Diluted	293.1	291.4	292.7	292.8
Net income (loss) per common share:
Basic	$ 2.80	$ 1.07	$ 5.08	$ 3.45
Diluted	$ 2.76	$ 1.06	$ 5.02	$ 3.41
Nonqualified Stock Options
Dilutive effects:
Stock-based compensation awards	1.7	1.4	1.8	1.1
Restricted Stock Units
Dilutive effects:
Stock-based compensation awards	1.9	1.6	1.9	1.6
Performance Share Awards
Dilutive effects:
Stock-based compensation awards	0.2	0.3	0.2	0.3