Pension plans - Fair value of plan assets (Detail) - Pension Plans, Defined Benefit [Member] - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 12,592	$ 18,620	$ 17,938
Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	602	992
Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	7,673	11,343
Fixed Maturity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,152	3,422
Investment Funds and Other [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,165	2,863
Quoted Prices (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	9,161	13,665
Quoted Prices (Level 1) [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	523	901
Quoted Prices (Level 1) [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	7,112	10,358
Quoted Prices (Level 1) [Member] | Fixed Maturity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,328	2,226
Quoted Prices (Level 1) [Member] | Investment Funds and Other [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	198	180
Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,618	2,280
Significant Other Observable Inputs (Level 2) [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	79	91
Significant Other Observable Inputs (Level 2) [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	321	660
Significant Other Observable Inputs (Level 2) [Member] | Fixed Maturity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	824	1,168
Significant Other Observable Inputs (Level 2) [Member] | Investment Funds and Other [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	394	361
Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	282	410
Significant Unobservable Inputs (Level 3) [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	240	325
Significant Unobservable Inputs (Level 3) [Member] | Fixed Maturity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		28
Significant Unobservable Inputs (Level 3) [Member] | Investment Funds and Other [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	42	57
Investments Carried at Net Asset Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,531	2,265
Investments Carried at Net Asset Value [Member] | Investment Funds and Other [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 1,531	$ 2,265