Investments - Past due commercial mortgage loans (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Mar. 31, 2025	Sep. 30, 2024	Dec. 31, 2024
Financing Receivable, Past Due [Line Items]
Financing Receivable, Excluding Accrued Interest, Nonaccrual	$ 14		$ 24
Financing Receivable, Nonaccrual, Interest Income	$ 0	$ 0
Commercial Portfolio Segment
Financing Receivable, Past Due [Line Items]
Financing Receivable, Threshold Past Due, Nonaccrual	90 days
Current | Commercial Portfolio Segment
Financing Receivable, Past Due [Line Items]
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss	$ 4,531		3,608
30 to 59 Days Past Due | Commercial Portfolio Segment
Financing Receivable, Past Due [Line Items]
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss	0		0
60 to 89 Days Past Due | Commercial Portfolio Segment
Financing Receivable, Past Due [Line Items]
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss	0		0
Greater than 90 Days Past Due | Commercial Portfolio Segment
Financing Receivable, Past Due [Line Items]
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss	14		24
Total Segment | Commercial Portfolio Segment
Financing Receivable, Past Due [Line Items]
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss	$ 4,545		$ 3,632