Winter Storm Uri (Details) - USD ($)	1 Months Ended	9 Months Ended
	Feb. 28, 2021	Jun. 30, 2021	Mar. 09, 2021	Sep. 30, 2020
Unusual or Infrequent Item, or Both [Line Items]
Aggregate natural gas purchases	$ 2,300,000,000
Regulatory assets		$ 2,527,012,000		$ 414,641,000
Winter Storm Uri
Unusual or Infrequent Item, or Both [Line Items]
Increase (decrease) in net operating loss carryforwards		469,400,000
Increase (decrease) in deferred income taxes		469,400,000
Federal net operating loss carryforward		804,700,000
State net operating loss carryforward		57,000,000.0
State net operating loss carryforward, federal effects		15,200,000
State tax credit carryforwards		1,800,000
State tax credit carryforwards, federal effects		500,000
Winter Storm Uri incremental costs
Unusual or Infrequent Item, or Both [Line Items]
Regulatory assets		2,093,779,000		$ 0
Winter Storm Uri incremental costs | Winter Storm Uri
Unusual or Infrequent Item, or Both [Line Items]
Regulatory assets		2,100,000,000
Winter Storm Uri incremental costs | Kansas | Winter Storm Uri
Unusual or Infrequent Item, or Both [Line Items]
Regulatory assets		77,100,000
Winter Storm Uri incremental costs | Texas | Winter Storm Uri
Unusual or Infrequent Item, or Both [Line Items]
Regulatory assets		2,016,700,000
Extraordinary Gas Cost | Winter Storm Uri
Unusual or Infrequent Item, or Both [Line Items]
Regulatory assets		$ 2,000,000,000.0
Senior Notes Due 2023
Unusual or Infrequent Item, or Both [Line Items]
Debt instrument, face amount			$ 2,200,000,000