Share-Based Compensation, Stock Equivalent Unit Plan (Details) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Equity Instruments Other than Options Activity [Roll Forward]
Balance at January 1 (in shares)	995,000
Granted (in shares)	500,000	503,000	522,000
Dividend equivalents (in shares)	45,000
Balance at December 31 (in shares)	939,000	995,000
Equity Instruments Other than Options, Weighted Average Grant Date Fair Value [Abstract]
Balance at January 1, weighted average grant date fair value (in dollars per share)	$ 38.48
Granted, weighted average grant date fair value (in dollars per share)	47.60	$ 41.02	$ 36.00
Dividend equivalents, weighted average grant date fair value (in dollars per share)	40.74
Balance at December 31, weighted average grant date fair value (in dollars per share)	$ 44.30	$ 38.48
Stock Equivalent Units [Member]
Equity Instruments Other than Options Activity [Roll Forward]
Balance at January 1 (in shares)	753,000
Granted (in shares)	36,000	51,000	49,000
Units distributed (in shares)	(123,000)
Dividend equivalents (in shares)	22,000
Balance at December 31 (in shares)	688,000	753,000
Equity Instruments Other than Options, Weighted Average Grant Date Fair Value [Abstract]
Balance at January 1, weighted average grant date fair value (in dollars per share)	$ 29.83
Granted, weighted average grant date fair value (in dollars per share)	45.44	$ 46.05	$ 40.68
Units distributed, weighted average grant date fair value (in dollars per share)	31.21
Dividend equivalents, weighted average grant date fair value (in dollars per share)	46.40
Balance at December 31, weighted average grant date fair value (in dollars per share)	$ 30.93	$ 29.83
Equity Instruments Other than Options, Additional Disclosures [Abstract]
Number of shares of common stock into which the share-based compensation can be converted (in shares)	1