Revenue - Additional Information (Detail) - USD ($) $ in Millions |
6 Months Ended | |
|---|---|---|
Jun. 30, 2019 |
Jun. 30, 2018 |
|
| Schedule of Investment Advisory Administration Fees and Securities Lending Revenue and Performance Fees by Type [line Items] | ||
| Estimated annual fixed minimum fees for currently outstanding contracts | $ 303 | $ 258 |
| Minimum [Member] | ||
| Schedule of Investment Advisory Administration Fees and Securities Lending Revenue and Performance Fees by Type [line Items] | ||
| Term of currently outstanding contracts | 1 year | |
| Maximum [Member] | ||
| Schedule of Investment Advisory Administration Fees and Securities Lending Revenue and Performance Fees by Type [line Items] | ||
| Term of currently outstanding contracts | 5 years |