Revenue Recognition (Disaggregation of Revenue) (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Disaggregation of Revenue [Line Items]
Customer revenues	$ 1,156.5	$ 952.4	$ 2,996.8	$ 2,458.9
Other revenues	26.7	33.6	59.7	72.7
Total Operating Revenues	1,183.2	986.0	3,056.5	2,531.6
Gas Distribution Operations
Disaggregation of Revenue [Line Items]
Customer revenues	741.4	569.9	2,175.3	1,697.0
Other revenues	(0.3)	4.4	2.5	13.1
Total Operating Revenues	741.1	574.3	2,177.8	1,710.1
Electric Operations
Disaggregation of Revenue [Line Items]
Customer revenues	415.1	382.3	821.5	761.5
Other revenues	22.0	21.2	45.7	44.5
Total Operating Revenues	437.1	403.5	867.2	806.0
Corporate and Other
Disaggregation of Revenue [Line Items]
Customer revenues	0.0	0.2	0.0	0.4
Other revenues	5.0	8.0	11.5	15.1
Total Operating Revenues	5.0	8.2	11.5	15.5
Residential
Disaggregation of Revenue [Line Items]
Customer revenues	602.0	510.5	1,717.4	1,413.2
Residential \| Gas Distribution Operations
Disaggregation of Revenue [Line Items]
Customer revenues	465.0	378.6	1,441.9	1,152.1
Residential \| Electric Operations
Disaggregation of Revenue [Line Items]
Customer revenues	137.0	131.9	275.5	261.1
Residential \| Corporate and Other
Disaggregation of Revenue [Line Items]
Customer revenues	0.0	0.0	0.0	0.0
Commercial
Disaggregation of Revenue [Line Items]
Customer revenues	295.3	255.4	786.3	649.7
Commercial \| Gas Distribution Operations
Disaggregation of Revenue [Line Items]
Customer revenues	160.6	125.4	517.1	396.9
Commercial \| Electric Operations
Disaggregation of Revenue [Line Items]
Customer revenues	134.7	130.0	269.2	252.8
Commercial \| Corporate and Other
Disaggregation of Revenue [Line Items]
Customer revenues	0.0	0.0	0.0	0.0
Industrial
Disaggregation of Revenue [Line Items]
Customer revenues	186.8	163.0	384.4	343.8
Industrial \| Gas Distribution Operations
Disaggregation of Revenue [Line Items]
Customer revenues	48.1	44.0	115.9	101.9
Industrial \| Electric Operations
Disaggregation of Revenue [Line Items]
Customer revenues	138.7	119.0	268.5	241.9
Industrial \| Corporate and Other
Disaggregation of Revenue [Line Items]
Customer revenues	0.0	0.0	0.0	0.0
Off-system
Disaggregation of Revenue [Line Items]
Customer revenues	59.1	17.0	77.8	31.4
Off-system \| Gas Distribution Operations
Disaggregation of Revenue [Line Items]
Customer revenues	59.1	17.0	77.8	31.4
Off-system \| Electric Operations
Disaggregation of Revenue [Line Items]
Customer revenues	0.0	0.0	0.0	0.0
Off-system \| Corporate and Other
Disaggregation of Revenue [Line Items]
Customer revenues	0.0	0.0	0.0	0.0
Miscellaneous
Disaggregation of Revenue [Line Items]
Customer revenues	13.3	6.5	30.9	20.8
Miscellaneous \| Gas Distribution Operations
Disaggregation of Revenue [Line Items]
Customer revenues	8.6	4.9	22.6	14.7
Miscellaneous \| Electric Operations
Disaggregation of Revenue [Line Items]
Customer revenues	4.7	1.4	8.3	5.7
Miscellaneous \| Corporate and Other
Disaggregation of Revenue [Line Items]
Customer revenues	$ 0.0	$ 0.2	$ 0.0	$ 0.4