Pension plans - Fair value of plan assets (Detail) - Pension Plans, Defined Benefit [Member] - USD ($)
$ in Millions |
Dec. 31, 2018 |
Dec. 31, 2017 |
Dec. 31, 2016 |
| Defined Benefit Plan Disclosure [Line Items] |
|
|
|
| Fair value of plan assets |
$ 14,959
|
$ 17,014
|
$ 15,397
|
| Cash and Cash Equivalents [Member] |
|
|
|
| Defined Benefit Plan Disclosure [Line Items] |
|
|
|
| Fair value of plan assets |
1,328
|
738
|
|
| Equity Securities [Member] |
|
|
|
| Defined Benefit Plan Disclosure [Line Items] |
|
|
|
| Fair value of plan assets |
7,671
|
9,824
|
|
| Government Obligations [Member] |
|
|
|
| Defined Benefit Plan Disclosure [Line Items] |
|
|
|
| Fair value of plan assets |
1,727
|
1,536
|
|
| Other Fixed Maturity Securities [Member] |
|
|
|
| Defined Benefit Plan Disclosure [Line Items] |
|
|
|
| Fair value of plan assets |
836
|
799
|
|
| Investment Funds and Other [Member] |
|
|
|
| Defined Benefit Plan Disclosure [Line Items] |
|
|
|
| Fair value of plan assets |
3,397
|
4,117
|
|
| Quoted Prices (Level 1) [Member] |
|
|
|
| Defined Benefit Plan Disclosure [Line Items] |
|
|
|
| Fair value of plan assets |
10,692
|
12,030
|
|
| Quoted Prices (Level 1) [Member] | Cash and Cash Equivalents [Member] |
|
|
|
| Defined Benefit Plan Disclosure [Line Items] |
|
|
|
| Fair value of plan assets |
1,197
|
594
|
|
| Quoted Prices (Level 1) [Member] | Equity Securities [Member] |
|
|
|
| Defined Benefit Plan Disclosure [Line Items] |
|
|
|
| Fair value of plan assets |
7,499
|
9,641
|
|
| Quoted Prices (Level 1) [Member] | Government Obligations [Member] |
|
|
|
| Defined Benefit Plan Disclosure [Line Items] |
|
|
|
| Fair value of plan assets |
1,654
|
1,497
|
|
| Quoted Prices (Level 1) [Member] | Other Fixed Maturity Securities [Member] |
|
|
|
| Defined Benefit Plan Disclosure [Line Items] |
|
|
|
| Fair value of plan assets |
172
|
148
|
|
| Quoted Prices (Level 1) [Member] | Investment Funds and Other [Member] |
|
|
|
| Defined Benefit Plan Disclosure [Line Items] |
|
|
|
| Fair value of plan assets |
170
|
150
|
|
| Significant Other Observable Inputs (Level 2) [Member] |
|
|
|
| Defined Benefit Plan Disclosure [Line Items] |
|
|
|
| Fair value of plan assets |
1,899
|
2,326
|
|
| Significant Other Observable Inputs (Level 2) [Member] | Cash and Cash Equivalents [Member] |
|
|
|
| Defined Benefit Plan Disclosure [Line Items] |
|
|
|
| Fair value of plan assets |
131
|
144
|
|
| Significant Other Observable Inputs (Level 2) [Member] | Equity Securities [Member] |
|
|
|
| Defined Benefit Plan Disclosure [Line Items] |
|
|
|
| Fair value of plan assets |
22
|
23
|
|
| Significant Other Observable Inputs (Level 2) [Member] | Government Obligations [Member] |
|
|
|
| Defined Benefit Plan Disclosure [Line Items] |
|
|
|
| Fair value of plan assets |
73
|
39
|
|
| Significant Other Observable Inputs (Level 2) [Member] | Other Fixed Maturity Securities [Member] |
|
|
|
| Defined Benefit Plan Disclosure [Line Items] |
|
|
|
| Fair value of plan assets |
631
|
619
|
|
| Significant Other Observable Inputs (Level 2) [Member] | Investment Funds and Other [Member] |
|
|
|
| Defined Benefit Plan Disclosure [Line Items] |
|
|
|
| Fair value of plan assets |
1,042
|
1,501
|
|
| Significant Unobservable Inputs (Level 3) [Member] |
|
|
|
| Defined Benefit Plan Disclosure [Line Items] |
|
|
|
| Fair value of plan assets |
456
|
466
|
|
| Significant Unobservable Inputs (Level 3) [Member] | Equity Securities [Member] |
|
|
|
| Defined Benefit Plan Disclosure [Line Items] |
|
|
|
| Fair value of plan assets |
150
|
160
|
|
| Significant Unobservable Inputs (Level 3) [Member] | Other Fixed Maturity Securities [Member] |
|
|
|
| Defined Benefit Plan Disclosure [Line Items] |
|
|
|
| Fair value of plan assets |
33
|
32
|
|
| Significant Unobservable Inputs (Level 3) [Member] | Investment Funds and Other [Member] |
|
|
|
| Defined Benefit Plan Disclosure [Line Items] |
|
|
|
| Fair value of plan assets |
273
|
274
|
|
| Investment Funds and Partnerships at Net Asset Value [Member] |
|
|
|
| Defined Benefit Plan Disclosure [Line Items] |
|
|
|
| Fair value of plan assets |
1,912
|
2,192
|
|
| Investment Funds and Partnerships at Net Asset Value [Member] | Investment Funds and Other [Member] |
|
|
|
| Defined Benefit Plan Disclosure [Line Items] |
|
|
|
| Fair value of plan assets |
$ 1,912
|
$ 2,192
|
|