Common Share Data (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Earnings Per Share [Abstract]
Numerator for basic and diluted earnings per share - income (loss) available to common stockholders		$ 397.7	$ 165.5	$ (207.0)	$ 577.7
Denominator for basic earnings per share - weighted-average shares (a)	[1]	297,523,559	299,418,182	298,915,853	299,341,472
Effect of dilutive securities - stock based compensation awards		252,756	1,334,810	0	1,239,292
Denominator for diluted earnings per shares adjusted weighted average shares and assumed conversions (a) (in shares)	[1]	297,776,315	300,752,992	298,915,853	300,580,764
Net income (loss) per share: Basic (in dollars per share)		$ 1.34	$ 0.55	$ (0.69)	$ 1.93
Net income (loss) per share: Diluted (in dollars per share)		$ 1.34	$ 0.55	$ (0.69)	$ 1.92
Stock based compensation awards [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive common stock equivalents excluded from earnings per share computations		8,065,611	1,163,250	9,570,275	3,268,875

[1] (a) In calculating earnings per share, pertinent accounting rules require that common shares owned by the Company's Employee Savings and Stock Ownership Plan that are not yet allocated to participants in the plan be excluded from the calculation. Such shares are issued and outstanding, and have the same voting and other rights applicable to all common shares.