Regulatory Matters - MEC - Regulatory Liabilities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Feb. 28, 2021	Dec. 31, 2020
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 6,960		$ 7,221
Cost of removal
Regulatory Liabilities [Line Items]
Regulatory liability, amortization period	26 years
Asset retirement obligations
Regulatory Liabilities [Line Items]
Regulatory liability, amortization period	31 years
MEC
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 1,080		1,111
Adjustment clause accounts receivable (payable)	$ 230	$ 245	22
MEC | Cost of removal
Regulatory Liabilities [Line Items]
Regulatory liability, amortization period	29 years
Regulatory liabilities	$ 394		466
MEC | Asset retirement obligations
Regulatory Liabilities [Line Items]
Regulatory liability, amortization period	31 years
Regulatory liabilities	$ 341		300
MEC | Iowa electric revenue sharing accrual
Regulatory Liabilities [Line Items]
Regulatory liability, amortization period	1 year
Regulatory liabilities	$ 115		0
MEC | Deferred income taxes
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 83		263
MEC | Employee benefit plans
Regulatory Liabilities [Line Items]
Regulatory liability, amortization period	9 years
Regulatory liabilities	$ 55		20
MEC | Pre-funded AFUDC on transmission MVPs
Regulatory Liabilities [Line Items]
Regulatory liability, amortization period	51 years
Regulatory liabilities	$ 34		35
MEC | Unrealized gain on regulated derivatives
Regulatory Liabilities [Line Items]
Regulatory liability, amortization period	1 year
Regulatory liabilities	$ 26		2
MEC | Other
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 32		$ 25