Pension and Other Postretirement Benefits - Schedule of Fair Value of Pension Plan Assets (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	$ 2,206	$ 2,426
Equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	369	704
Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	242	551
Long/Short Equity Hedge Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets		8
Private Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	127	145
Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	1,544	1,392
Intermediate and Long Duration Government Credit [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	1,416	1,236
Cash and Cash Equivalent Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	128	156
Other Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	293	330
Real Estate Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	274	302
Other Investments, Other [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	19	28
Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	546	519
Level 1 [Member] | Equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	108	71
Level 1 [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	108	71
Level 1 [Member] | Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	417	428
Level 1 [Member] | Intermediate and Long Duration Government Credit [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	403	390
Level 1 [Member] | Cash and Cash Equivalent Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	14	38
Level 1 [Member] | Other Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	21	20
Level 1 [Member] | Real Estate Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	21	20
Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	517	426
Level 2 [Member] | Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	517	426
Level 2 [Member] | Intermediate and Long Duration Government Credit [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	517	426
Net Asset Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	1,143	1,481
Net Asset Value [Member] | Equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	261	633
Net Asset Value [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	134	480
Net Asset Value [Member] | Long/Short Equity Hedge Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets		8
Net Asset Value [Member] | Private Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	127	145
Net Asset Value [Member] | Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	610	538
Net Asset Value [Member] | Intermediate and Long Duration Government Credit [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	496	420
Net Asset Value [Member] | Cash and Cash Equivalent Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	114	118
Net Asset Value [Member] | Other Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	272	310
Net Asset Value [Member] | Real Estate Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	253	282
Net Asset Value [Member] | Other Investments, Other [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	$ 19	$ 28