Commitments, contingencies, and guarantees (Narrative) (Detail) € in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2022 EUR (€)	Oct. 06, 2022 USD ($)
Financial Instruments Owned and Pledged as Collateral [Line Items]
Derivative Liability, Fair Value, Amount Subject to a Master Netting Agreement	$ 60	$ 123
Hedged Liability, Fair Value Hedge	1,600			€ 1,500
Securities Sold under Agreements to Repurchase	1,419	1,406
Repurchase agreements	$ 1,419	$ 1,406
Concentration Risk Percentage Marsh	11.00%	12.00%	12.00%	11.00%
Purchase Commitment, Remaining Minimum Amount Committed	$ 770	$ 771
Carrying value of limited partnerships and partially-owned investment companies included in other investments	12,000	9,800
Funding commitments relating to limited partnerships and partially-owned investment companies	7,400	7,200
Line of Credit Facility, Maximum Borrowing Capacity	2,700				$ 3,000
Line of Credit Facility, Current Borrowing Capacity	4,000
Line of Credit Facility, Capacity Available for Specific Purpose Other than for Trade Purchases	3,000
Operating Lease, Right-of-Use Asset	607	445
Operating Lease, Liability	$ 633	484
Operating Lease, Weighted Average Remaining Lease Term	7 years 9 months 18 days			7 years 9 months 18 days
Operating Lease, Weighted Average Discount Rate, Percent	3.50%			3.50%
Deposit Assets	$ 96	$ 101
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]
Operating Lease, Liability, Statement of Financial Position [Extensible List]	Other Liabilities	Other Liabilities		Other Liabilities
Operating Lease, Cost	$ 161	$ 149	$ 152
Lessee, Lease Not Yet Commenced, Noncurrent Amount	1,200
Interest expense	570	492	516
Other Comprehensive Income (Loss), before Tax	(11,664)	$ (2,946)	$ 2,666
Letter of Credit [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Line of Credit Facility, Amount Outstanding	1,400
Fair Value Hedging
Financial Instruments Owned and Pledged as Collateral [Line Items]
OCI, before Reclassifications, Net of Tax, Attributable to Parent	17
Derivative Instruments, Loss Reclassified from Accumulated OCI into Income, Effective Portion	105
Interest expense	5
Other Comprehensive Income (Loss), before Tax	(83)
Net Investment Hedging
Financial Instruments Owned and Pledged as Collateral [Line Items]
OCI, before Reclassifications, Net of Tax, Attributable to Parent	(53)
Interest expense	4
Other Comprehensive Income (Loss), before Tax	$ (57)