Pension Plans and Other Postretirement Benefits - Fair Values of Company's Pension Plan Assets by Asset Category (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	$ 3,203	$ 3,141
Interest and dividend receivable on plan assets	$ 5	$ 4
Investment Grade Bonds
Defined Benefit Plan Disclosure [Line Items]
Investment in mutual funds	73.00%	73.00%
High-Yielding Bonds
Defined Benefit Plan Disclosure [Line Items]
Investment in mutual funds	27.00%	27.00%
Level 1
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	$ 2,028	$ 2,164
Level 2
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	690	533
Level 3
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	485	444
Money-market investments
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	76	65
Money-market investments | Level 1
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	50	41
Money-market investments | Level 2
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	26	24
Money-market investments | Level 3
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	0	0
Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	1,355	1,449
Equity Securities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	1,355	1,449
Equity Securities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	0	0
Equity Securities | Level 3
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	0	0
M&T
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	135	112
M&T | Level 1
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	135	112
M&T | Level 2
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	0	0
M&T | Level 3
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	0	0
Domestic Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	440	512
Domestic Equity Securities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	440	512
Domestic Equity Securities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	0	0
Domestic Equity Securities | Level 3
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	0	0
International Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	17	17
International Equity Securities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	17	17
International Equity Securities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	0	0
International Equity Securities | Level 3
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	0	0
Domestic Mutual Fund
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	282	307
Domestic Mutual Fund | Level 1
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	282	307
Domestic Mutual Fund | Level 2
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	0	0
Domestic Mutual Fund | Level 3
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	0	0
International Mutual Fund
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	481	501
International Mutual Fund | Level 1
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	481	501
International Mutual Fund | Level 2
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	0	0
International Mutual Fund | Level 3
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	0	0
Total Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	944	959
Total Debt Securities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	425	450
Total Debt Securities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	519	509
Total Debt Securities | Level 3
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	0	0
Corporate Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	222	227
Corporate Debt Securities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	0	0
Corporate Debt Securities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	222	227
Corporate Debt Securities | Level 3
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	0	0
Government
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	281	276
Government | Level 1
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	0	0
Government | Level 2
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	281	276
Government | Level 3
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	0	0
International
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	16	6
International | Level 1
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	0	0
International | Level 2
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	16	6
International | Level 3
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	0	0
Domestic Mutual Fund Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	425	450
Domestic Mutual Fund Debt Securities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	425	450
Domestic Mutual Fund Debt Securities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	0	0
Domestic Mutual Fund Debt Securities | Level 3
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	0	0
Other Investments
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	828	668
Other Investments | Level 1
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	198	224
Other Investments | Level 2
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	145	0
Other Investments | Level 3
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	485	444
Diversified mutual fund
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	110	110
Diversified mutual fund | Level 1
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	110	110
Diversified mutual fund | Level 2
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	0	0
Diversified mutual fund | Level 3
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	0	0
Common Collective Trust
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	145
Common Collective Trust | Level 1
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	0
Common Collective Trust | Level 2
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	145
Common Collective Trust | Level 3
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	0
Real estate partnerships
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	31	29
Real estate partnerships | Level 1
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	5	7
Real estate partnerships | Level 2
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	0	0
Real estate partnerships | Level 3
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	26	22
Private equity/debt
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	265	235
Private equity/debt | Level 1
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	0	0
Private equity/debt | Level 2
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	0	0
Private equity/debt | Level 3
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	265	235
Hedge funds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	267	285
Hedge funds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	83	107
Hedge funds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	0	0
Hedge funds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	184	178
Guaranteed deposit fund
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	10	9
Guaranteed deposit fund | Level 1
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	0	0
Guaranteed deposit fund | Level 2
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	0	0
Guaranteed deposit fund | Level 3
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	$ 10	$ 9