Investment gains/losses - Narrative (Detail) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2018 |
Dec. 31, 2017 |
Dec. 31, 2016 |
|
| Gain (Loss) on Securities [Line Items] | |||
| Sales and redemptions of equity securities | $ 18,783 | $ 19,512 | $ 28,464 |
| Taxable gains on sales of equity securities | 3,300 | ||
| Investment gains (losses) | $ (22,155) | 1,410 | 7,553 |
| Bank of America Corporation [Member] | Non-Cumulative Perpetual Preferred Stock [Member] | |||
| Gain (Loss) on Securities [Line Items] | |||
| Investment gains (losses) | $ 1,000 | ||
| Wm Wrigley Jr Company, The Kraft Heinz Company, and Dow Chemical Company [Member] | Preferred Stock and Common Stock [Member] | |||
| Gain (Loss) on Securities [Line Items] | |||
| Gross gains | 4,200 | ||
| Duracell Company [Member] | Procter & Gamble Company [Member] | Common Stock [Member] | |||
| Gain (Loss) on Securities [Line Items] | |||
| Gross gains | $ 1,100 | ||