Accumulated other comprehensive income (Detail) - USD ($)
$ in Millions |
12 Months Ended |
Dec. 31, 2018 |
Dec. 31, 2017 |
Dec. 31, 2016 |
| Accumulated Other Comprehensive Income (Loss) [Line Items] |
|
|
|
| Beginning Balance |
$ 351,954
|
$ 285,428
|
$ 257,696
|
| Ending Balance |
352,500
|
351,954
|
285,428
|
| Unrealized appreciation of investments, net [Member] |
|
|
|
| Accumulated Other Comprehensive Income (Loss) [Line Items] |
|
|
|
| Beginning Balance |
62,093
|
43,176
|
38,598
|
| Reclassifications to retained earnings upon adoption of new accounting standards |
(61,340)
|
|
|
| Other comprehensive income, net before reclassifications |
(183)
|
19,826
|
9,011
|
| Reclassifications before income taxes |
(253)
|
(1,399)
|
(6,820)
|
| Applicable income taxes |
53
|
490
|
2,387
|
| Ending Balance |
370
|
62,093
|
43,176
|
| Foreign currency translation [Member] |
|
|
|
| Accumulated Other Comprehensive Income (Loss) [Line Items] |
|
|
|
| Beginning Balance |
(3,114)
|
(5,268)
|
(3,856)
|
| Reclassifications to retained earnings upon adoption of new accounting standards |
(65)
|
|
|
| Other comprehensive income, net before reclassifications |
(1,424)
|
2,151
|
(1,412)
|
| Reclassifications before income taxes |
|
3
|
|
| Ending Balance |
(4,603)
|
(3,114)
|
(5,268)
|
| Prior service and actuarial gains/losses of defined benefit pension plans [Member] |
|
|
|
| Accumulated Other Comprehensive Income (Loss) [Line Items] |
|
|
|
| Beginning Balance |
(420)
|
(593)
|
(762)
|
| Reclassifications to retained earnings upon adoption of new accounting standards |
36
|
|
|
| Other comprehensive income, net before reclassifications |
(513)
|
65
|
94
|
| Reclassifications before income taxes |
116
|
155
|
104
|
| Applicable income taxes |
(35)
|
(47)
|
(29)
|
| Ending Balance |
(816)
|
(420)
|
(593)
|
| Other AOCI transactions [Member] |
|
|
|
| Accumulated Other Comprehensive Income (Loss) [Line Items] |
|
|
|
| Beginning Balance |
12
|
(17)
|
2
|
| Reclassifications to retained earnings upon adoption of new accounting standards |
(6)
|
|
|
| Other comprehensive income, net before reclassifications |
25
|
16
|
(48)
|
| Reclassifications before income taxes |
5
|
19
|
51
|
| Applicable income taxes |
(2)
|
(6)
|
(22)
|
| Ending Balance |
34
|
12
|
(17)
|
| Accumulated other comprehensive income [Member] |
|
|
|
| Accumulated Other Comprehensive Income (Loss) [Line Items] |
|
|
|
| Beginning Balance |
58,571
|
37,298
|
33,982
|
| Reclassifications to retained earnings upon adoption of new accounting standards |
(61,375)
|
|
|
| Other comprehensive income, net before reclassifications |
(2,095)
|
22,058
|
7,645
|
| Reclassifications before income taxes |
(132)
|
(1,222)
|
(6,665)
|
| Applicable income taxes |
16
|
437
|
2,336
|
| Ending Balance |
$ (5,015)
|
$ 58,571
|
$ 37,298
|