Accounting for Derivative Instruments and Hedging Activities - Net Notional Volume Buy/Sell of Open Derivative Transactions (Details) certificate in Millions, bbl in Millions, T in Millions, MWh in Millions, MMBTU in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2021 USD ($) MWh MMBTU certificate T bbl	Dec. 31, 2020 USD ($) MWh MMBTU certificate T bbl
Long | Emissions
Derivative [Line Items]
Derivative, nonmonetary notional amount, mass (ton) | T	1	1
Long | Renewables Energy Certificates
Derivative [Line Items]
Derivative, non-monetary notional amount (in shares) | certificate	13	5
Long | Coal
Derivative [Line Items]
Derivative, nonmonetary notional amount, mass (ton) | T	19	2
Long | Oil
Derivative [Line Items]
Derivative, nonmonetary notional amount, volume (in barrels) | bbl	1	0
Long | Power
Derivative [Line Items]
Derivative, nonmonetary notional amount, energy measure in (millions of btu) and (megawatt hours) | MWh	185	57
Long | Foreign Exchange
Derivative [Line Items]
Derivative, notional amount (usd) | $	$ 279	$ 0
Short | Natural Gas
Derivative [Line Items]
Derivative, nonmonetary notional amount, energy measure in (millions of btu) and (megawatt hours) | MMBTU	813	286
Short | Capacity
Derivative [Line Items]
Derivative, nonmonetary notional amount, energy measure in (millions of btu) and (megawatt hours) | MWh	0	1