Pension Plans and Other Postretirement Benefits - Changes in Level 3 Pension Plan Assets Measured at Fair Value on Recurring Basis (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2024 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	$ 3,141
Fair value of plan assets at end of year	3,203
Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	444
Net Purchases (Sales)	(10)
Realized and unrealized gains (losses)	51
Fair value of plan assets at end of year	485
Real estate partnerships
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	29
Fair value of plan assets at end of year	31
Real estate partnerships | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	22
Net Purchases (Sales)	3
Realized and unrealized gains (losses)	1
Fair value of plan assets at end of year	26
Private equity/debt
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	235
Fair value of plan assets at end of year	265
Private equity/debt | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	235
Net Purchases (Sales)	5
Realized and unrealized gains (losses)	25
Fair value of plan assets at end of year	265
Hedge funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	285
Fair value of plan assets at end of year	267
Hedge funds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	178
Net Purchases (Sales)	(18)
Realized and unrealized gains (losses)	24
Fair value of plan assets at end of year	184
Guaranteed deposit fund
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	9
Fair value of plan assets at end of year	10
Guaranteed deposit fund | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	9
Net Purchases (Sales)	0
Realized and unrealized gains (losses)	1
Fair value of plan assets at end of year	$ 10