Operations and Significant Accounting Policies - Supplemental Statement of Cash Flow Information - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Supplemental Cash Flow Information [Abstract]
Cash Paid During the Period for Interest – Net of Amounts Capitalized		$ 66.8	$ 62.0	$ 63.5
Recognition of Right-of-use Assets and Lease Liabilities	[1]	0.0	0.0	28.7
Noncash Investing and Financing Activities [Abstract]
Increase (Decrease) in Accounts Payable for Capital Additions to Property, Plant and Equipment		(14.0)	(67.0)	33.9
Reclassification of Redeemable Non-Controlling Interest to Current Liabilities	[2]	30.6	0.0	0.0
Capitalized Asset Retirement Costs		16.9	4.1	20.7
AFUDC–Equity		$ 2.6	$ 1.9	$ 2.3

[1] Amount of the right-of-use asset and lease liability recognized with the adoption of an accounting standards update for leases.

[2] Amount reclassified to Current Liabilities resulting from the exercise of an option to buy out a non-controlling interest.