Fair value measurements (Carrying Values And Fair Values Of Financial Instruments Not Measured At Fair Value) (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Private debt held-for-investment	$ 2,619	$ 2,553
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Repurchase agreements	3,048	2,833
Short-term debt	1,571	1,460
Long-term debt	14,560	13,035
Total liabilities	180,437	166,991
Portion at Other than Fair Value Measurement | Level 1
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Private debt held-for-investment	0	0
Total assets	0	0
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Repurchase agreements	0	0
Short-Term Debt, Fair Value	0	0
Long-term Debt, Fair Value	0	0
Junior Subordinated Debenture Owed to Unconsolidated Subsidiary Trust	0	0
Liabilities, Fair Value Disclosure	0	0
Portion at Other than Fair Value Measurement | Level 2
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Private debt held-for-investment	0	0
Total assets	0	0
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Repurchase agreements	3,048	2,833
Short-Term Debt, Fair Value	1,560	1,431
Long-term Debt, Fair Value	13,645	11,924
Junior Subordinated Debenture Owed to Unconsolidated Subsidiary Trust	377	365
Liabilities, Fair Value Disclosure	18,630	16,553
Portion at Other than Fair Value Measurement | Level 3
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Private debt held-for-investment	2,650	2,560
Total assets	2,650	2,560
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Repurchase agreements	0	0
Short-Term Debt, Fair Value	0	0
Long-term Debt, Fair Value	0	0
Junior Subordinated Debenture Owed to Unconsolidated Subsidiary Trust	0	0
Liabilities, Fair Value Disclosure	0	0
Portion at Other than Fair Value Measurement | Total Level 1, Level 2, and Level 3
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Private debt held-for-investment	2,650	2,560
Total assets	2,650	2,560
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Repurchase agreements	3,048	2,833
Short-Term Debt, Fair Value	1,560	1,431
Long-term Debt, Fair Value	13,645	11,924
Junior Subordinated Debenture Owed to Unconsolidated Subsidiary Trust	377	365
Liabilities, Fair Value Disclosure	18,630	16,553
Reported Value Measurement [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Private debt held-for-investment	2,619	2,553
Total assets	2,619	2,553
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Repurchase agreements	3,048	2,833
Short-term debt	1,571	1,460
Long-term debt	14,560	13,035
Junior Subordinated Debenture Owed to Unconsolidated Subsidiary Trust	309	308
Liabilities, Fair Value Disclosure	$ 19,488	$ 17,636