Fair value measurements - Significant unobservable inputs (Detail) - Significant Unobservable Inputs (Level 3) [Member] - USD ($)
$ in Millions |
12 Months Ended |
Dec. 31, 2018 |
Dec. 31, 2017 |
Dec. 31, 2016 |
| Fair Value Measurements Significant Unobservable Inputs [Line Items] |
|
|
|
| Net derivative contract liabilities - Beginning Balance |
$ (2,069)
|
$ (2,824)
|
$ (3,785)
|
| Net derivative contract liabilities - Gains (losses) included in earnings |
(118)
|
888
|
880
|
| Net derivative contract liabilities - Gains (losses) included in other comprehensive income |
2
|
(3)
|
(2)
|
| Net derivative contract liabilities - Gains (losses) included in regulatory assets and liabilities |
3
|
(1)
|
(11)
|
| Net derivative contract liabilities - Acquisitions |
3
|
|
|
| Net derivative contract liabilities - Dispositions and settlements |
(164)
|
(129)
|
(101)
|
| Net derivative contract liabilities - Transfers into/out of Level 3 |
|
|
195
|
| Net derivative contract liabilities - Ending Balance |
(2,343)
|
(2,069)
|
(2,824)
|
| Investments in Equity and Fixed Maturity Securities [Member] |
|
|
|
| Fair Value Measurements Significant Unobservable Inputs [Line Items] |
|
|
|
| Beginning Balance |
6
|
17,321
|
21,503
|
| Gains (losses) included in earnings |
|
|
3,593
|
| Gains (losses) included in other comprehensive income |
|
1,157
|
872
|
| Acquisitions |
302
|
|
10
|
| Dispositions and settlements |
(1)
|
(59)
|
(8,656)
|
| Transfers into/out of Level 3 |
|
(18,413)
|
(1)
|
| Ending Balance |
$ 307
|
$ 6
|
$ 17,321
|