Equity (Common Stock Changes in Number of Shares Issued, Held in Treasury and Outstanding) (Details)		1 Months Ended	12 Months Ended
	Aug. 02, 2019 USD ($) shares	Sep. 30, 2009 USD ($) shares	Dec. 31, 2019 USD ($) shares	Dec. 31, 2018 shares	Dec. 31, 2017 shares
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			660,111,339
Ending Balance			666,305,189	660,111,339
Incremental Common Shares Attributable to Dilutive Effect of Conversion of Debt Securities			3,600,000	5,900,000	5,800,000
Issued
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			660,100,000	660,100,000	660,100,000
Common Stock issued			6,200,000	0.0	0.0
Common Stock acquired			0.0	0.0	0.0
Stock-based compensation programs			0.0	0.0	0.0
Ending Balance			666,300,000	660,100,000	660,100,000
Held In Treasury
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			249,400,000	237,500,000	230,500,000
Common Stock issued			(5,500,000)	0.0	0.0
Common Stock acquired			27,200,000	14,900,000	11,500,000
Stock-based compensation programs			(3,600,000)	(3,000,000.0)	(4,500,000)
Ending Balance			267,500,000	249,400,000	237,500,000
Outstanding
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			410,700,000	422,600,000	429,600,000
Common Stock issued			11,700,000	0.0	0.0
Common Stock acquired			(27,200,000)	(14,900,000)	(11,500,000)
Stock-based compensation programs			3,600,000	3,000,000.0	4,500,000
Ending Balance			398,800,000	410,700,000	422,600,000
Exhangeable Surplus Notes | Long-term Debt
Class of Stock [Line Items]
Debt Instrument, Face Amount | $		$ 500,000,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Incremental Common Shares Attributable to Dilutive Effect of Conversion of Debt Securities	6,200,000	5,100,000
Debt Instrument, Convertible, Conversion Ratio	12.3877	10.1235
Surplus Notes | $	$ 1,000	$ 1,000	$ 1,000
Common Stock Held in Treasury | Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock Issued During Period, Shares, Acquisitions			5,500,000