Consolidated Statement of Equity - USD ($) $ in Millions	Total	Retained Earnings [Member]	Accumulated Other Comprehensive Loss [Member]	Common Stock [Member]	Non-Controlling Interest in Subsidiaries [Member]
Beginning Balance at Dec. 31, 2015	$ 1,822.4	$ 573.3	$ (24.5)	$ 1,271.4	$ 2.2
Comprehensive Income
Net Income	155.8	155.3			0.5
Other Comprehensive Income – Net of Taxes
Unrealized Gain (Loss) on Securities	(0.2)		(0.2)
Defined Benefit Pension and Other Postretirement Plans	(3.5)		(3.5)
Total Comprehensive Income	152.1
Common Stock Issued	35.9			35.9
Common Stock Retired	(8.0)			(8.0)
Dividends Declared	(102.7)	(102.7)
Acquisition of Non-Controlling Interest	(6.7)			4.0	(2.7)
Ending Balance at Dec. 31, 2016	1,893.0	625.9	(28.2)	1,295.3	0.0
Comprehensive Income
Net Income	172.2	172.2			0.0
Other Comprehensive Income – Net of Taxes
Unrealized Gain (Loss) on Securities	0.9		0.9
Defined Benefit Pension and Other Postretirement Plans	4.7		4.7
Total Comprehensive Income	177.8
Common Stock Issued	106.1			106.1
Dividends Declared	(108.7)	(108.7)
Ending Balance at Dec. 31, 2017	2,068.2	689.4	(22.6)	1,401.4	0.0
Consolidated Statement of Equity [Roll Forward]
Adjustments to Opening Balance – Net of Income Taxes (a)	0.5	6.1	(5.6)	0.0	0.0
Beginning Balance - Adjusted	2,068.7	695.5	(28.2)	1,401.4	0.0
Comprehensive Income
Net Income	174.1	174.1			0.0
Other Comprehensive Income – Net of Taxes
Unrealized Gain (Loss) on Securities	(0.1)		(0.1)
Defined Benefit Pension and Other Postretirement Plans	1.0		1.0
Total Comprehensive Income	175.0
Common Stock Issued	27.1			27.1
Dividends Declared	(115.0)	(115.0)
Ending Balance at Dec. 31, 2018	$ 2,155.8	$ 754.6	$ (27.3)	$ 1,428.5	$ 0.0