Investments - Summary of Carrying Value of Total Investments (Parenthetical) (Detail) - USD ($) $ in Millions |
Mar. 31, 2018 |
Dec. 31, 2017 |
|---|---|---|
| Investment [Line Items] | ||
| Total trading investments | $ 835 | |
| Equity securities | $ 648 | |
| Consolidated Sponsored Investment Funds [Member] | Debt securities [Member] | ||
| Investment [Line Items] | ||
| Total trading investments | 266 | 267 |
| Consolidated Sponsored Investment Funds [Member] | Equity securities [Member] | ||
| Investment [Line Items] | ||
| Total trading investments | $ 245 | |
| Equity securities | $ 284 |