Income Taxes (Summary of Deductible Loss and Credit Carryforwards) (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2021 USD ($)
Investments Owned Federal Income Tax Note [Line Items]
Loss and Credit Carryforwards, Deductible Amount	$ 3,507
Loss and Credit Carryforwards, Deferred Tax Asset	374
Federal
Investments Owned Federal Income Tax Note [Line Items]
Loss Carryforwards, Deductible Amount	890
Loss Carryforwards, Deferred Tax Asset	$ 187
Loss Carryforwards, Expiration Period	2037
Federal | Production and Other Credits
Investments Owned Federal Income Tax Note [Line Items]
Credit Carryforwards, Deductible Amount	$ 0
Credit Carryforwards, Deferred Tax Asset	$ 29
Federal | Minimum [Member] | Production and Other Credits
Investments Owned Federal Income Tax Note [Line Items]
Credit Carryforwards, Expiration Period	2035
Federal | Maximum [Member] | Production and Other Credits
Investments Owned Federal Income Tax Note [Line Items]
Credit Carryforwards, Expiration Period	2041
State
Investments Owned Federal Income Tax Note [Line Items]
Loss Carryforwards, Deductible Amount	$ 2,617
Loss Carryforwards, Deferred Tax Asset	131
State | Investment and Other Credits
Investments Owned Federal Income Tax Note [Line Items]
Credit Carryforwards, Deductible Amount	0
Credit Carryforwards, Deferred Tax Asset	$ 27
State | Minimum [Member]
Investments Owned Federal Income Tax Note [Line Items]
Loss Carryforwards, Expiration Period	2037
State | Minimum [Member] | Investment and Other Credits
Investments Owned Federal Income Tax Note [Line Items]
Credit Carryforwards, Expiration Period	2026
State | Maximum [Member]
Investments Owned Federal Income Tax Note [Line Items]
Loss Carryforwards, Expiration Period	2040
State | Maximum [Member] | Investment and Other Credits
Investments Owned Federal Income Tax Note [Line Items]
Credit Carryforwards, Expiration Period	2031