Commitments, contingencies, and guarantees (Narrative) (Detail) € in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2024 EUR (€)
Financial Instruments Owned and Pledged as Collateral [Line Items]
Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]
Derivative Liability, Subject to Master Netting Arrangement, after Offset	$ (199)	$ 115
Securities Sold under Agreements to Repurchase	2,731	2,833
Repurchase agreements	$ 2,731	$ 2,833
Concentration Risk Percentage Marsh	11.00%	11.00%	11.00%	11.00%
Purchase Commitment, Remaining Minimum Amount Committed	$ 1,300	$ 1,000
Carrying value of limited partnerships and partially-owned investment companies included in other investments	14,500	13,900
Other Commitment	6,400	6,200
Line of Credit Facility, Current Borrowing Capacity	4,100
Line of Credit Facility, Capacity Available for Specific Purpose Other than for Trade Purchases	3,000
Operating Lease, Right-of-Use Asset	824	784
Operating Lease, Liability	$ 942	$ 832
Operating Lease, Weighted Average Remaining Lease Term	13 years 3 months 18 days			13 years 3 months 18 days
Operating Lease, Weighted Average Discount Rate, Percent	4.60%			4.60%
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]
Operating Lease, Liability, Statement of Financial Position [Extensible List]
Operating Lease, Cost	$ 214	$ 181	$ 161
Lessee, Lease Not Yet Commenced, Noncurrent Amount	400
Group Syndicated Credit Facility [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Line of Credit Facility, Current Borrowing Capacity	3,000
Long-Term Debt [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Hedged Liability, Fair Value Hedge	$ 1,600			€ 1,500
Revenue Benchmark
Financial Instruments Owned and Pledged as Collateral [Line Items]
Concentration Risk, Customer	accounted for more than 10 percent	accounted for more than 10 percent	accounted for more than 10 percent
Letter of Credit [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Line of Credit Facility, Amount Outstanding	$ 978	$ 948