Segment Information - Amortization of Deferred Policy Acquisition Costs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Segment Reporting Information [Line Items]
Amortization of deferred policy acquisition costs ("DAC")	$ 2,044	$ 1,824	$ 1,668
Operating Segments | P&C Commercial Lines
Segment Reporting Information [Line Items]
Amortization of deferred policy acquisition costs ("DAC")	1,779	1,563	1,398
Operating Segments | P&C Personal Lines
Segment Reporting Information [Line Items]
Amortization of deferred policy acquisition costs ("DAC")	231	228	230
Operating Segments | Group Benefits [Member]
Segment Reporting Information [Line Items]
Amortization of deferred policy acquisition costs ("DAC")	$ 34	$ 33	$ 40