Revenue - Schedule of Estimated Investment Advisory, Administration Fees Expected to be Recognized in Future, Related to Unsatisfied Portion of Performance Obligations (Detail) - Investment Advisory, Administration Fees and Securities Lending Revenue [Member] - USD ($) $ in Millions	Mar. 31, 2025	Mar. 31, 2024
Schedule of Investment Advisory Administration Fees and Performance Fees by Type [line Items]
Revenue, Remaining Performance Obligation	$ 1,393	$ 659
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2024-04-01
Schedule of Investment Advisory Administration Fees and Performance Fees by Type [line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period		9 months
Revenue, Remaining Performance Obligation		$ 152
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2025-01-01
Schedule of Investment Advisory Administration Fees and Performance Fees by Type [line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period		1 year
Revenue, Remaining Performance Obligation		$ 180
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2025-04-01
Schedule of Investment Advisory Administration Fees and Performance Fees by Type [line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	9 months
Revenue, Remaining Performance Obligation	$ 369
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2026-01-01
Schedule of Investment Advisory Administration Fees and Performance Fees by Type [line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	1 year	1 year
Revenue, Remaining Performance Obligation	$ 445	$ 159
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2027-01-01
Schedule of Investment Advisory Administration Fees and Performance Fees by Type [line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	1 year	1 year
Revenue, Remaining Performance Obligation	$ 416	$ 119
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2028-01-01
Schedule of Investment Advisory Administration Fees and Performance Fees by Type [line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	1 year	1 year
Revenue, Remaining Performance Obligation	$ 131	$ 49
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2029-01-01
Schedule of Investment Advisory Administration Fees and Performance Fees by Type [line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	1 year
Revenue, Remaining Performance Obligation	$ 32