New Accounting Pronouncements (Narrative) (Details) $ in Millions	9 Months Ended
	Sep. 30, 2018 USD ($)
Accounting Standards Update 2018-02 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Cumulative effect on retained earnings, net of tax	$ 6.5
Accounting Standards Update 2016-01 And 2018-03 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Cumulative effect adjustment benefit to retained earnings	97.8
Cumulative effect on retained earnings, net of tax	95.2
Gains on partnership investments at NAV	2.6
Accounting Standards Update 2016-02 And 2018-11 [Member] | Minimum [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Cumulative effect to increase assets and liabilities	40.0
Accounting Standards Update 2016-02 And 2018-11 [Member] | Maximum [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Cumulative effect to increase assets and liabilities	$ 50.0