Investments - Summary of Carrying Value of Total Investments (Parenthetical) (Detail) - USD ($) $ in Millions |
Jun. 30, 2019 |
Dec. 31, 2018 |
|---|---|---|
| Investments [Line Items] | ||
| Equity securities | $ 537 | $ 452 |
| Consolidated Sponsored Investment Funds [Member] | Debt securities [Member] | ||
| Investments [Line Items] | ||
| Total trading investments | 143 | 233 |
| Consolidated Sponsored Investment Funds [Member] | Equity securities [Member] | ||
| Investments [Line Items] | ||
| Equity securities | $ 309 | $ 291 |