Fair value measurements (Carrying Values And Fair Values Of Financial Instruments Not Measured At Fair Value) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Private debt held-for-investment	$ 2,708	$ 2,553
Total assets (preliminary)	234,867	230,682
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Repurchase agreements	3,022	2,833
Short-term debt	2,265	1,460
Long-term debt	13,248	13,035
Total liabilities	170,436	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 (preliminary)	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
Total liabilities	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 (preliminary)	0	0
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Repurchase agreements	3,022	2,833
Short-Term Debt, Fair Value	2,228	1,431
Long-term Debt, Fair Value	11,930	11,924
Junior Subordinated Debenture Owed to Unconsolidated Subsidiary Trust	365	365
Total liabilities	17,545	16,553
Portion at Other than Fair Value Measurement | Level 3
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Private debt held-for-investment	2,733	2,560
Total assets (preliminary)	2,733	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
Total liabilities	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	2,733	2,560
Total assets (preliminary)	2,733	2,560
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Repurchase agreements	3,022	2,833
Short-Term Debt, Fair Value	2,228	1,431
Long-term Debt, Fair Value	11,930	11,924
Junior Subordinated Debenture Owed to Unconsolidated Subsidiary Trust	365	365
Total liabilities	17,545	16,553
Reported Value Measurement [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Private debt held-for-investment	2,708	2,553
Total assets (preliminary)	2,708	2,553
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Repurchase agreements	3,022	2,833
Short-term debt	2,265	1,460
Long-term debt	13,248	13,035
Junior Subordinated Debenture Owed to Unconsolidated Subsidiary Trust	309	308
Total liabilities	$ 18,844	$ 17,636