Operations and Significant Accounting Policies - Supplemental Statement of Cash Flows Information - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Supplemental Cash Flow Information [Abstract]
Cash Paid for Interest – Net of Amounts Capitalized	$ 48.8	$ 53.5
Recognition of Right-of-use Assets and Lease Liabilities	0.0	30.4
Noncash Investing and Financing Activities [Abstract]
Increase (Decrease) in Accounts Payable for Capital Additions to Property, Plant and Equipment	(88.4)	6.3
Capitalized Asset Retirement Costs	2.1	16.6
AFUDC–Equity	$ 1.8	$ 1.9