Fair Value of Assets and Liabilities (Balances of Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) - USD ($) $ in Millions	Jun. 30, 2025		Dec. 31, 2024
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	$ 86,043	[1]	$ 77,617	[2]
Equity Method Investments, Fair Value Disclosure	155	[1]	155	[2]
Funds withheld at interest embedded derivatives	(250)	[1]	(215)	[2]
Funds Held Under Reinsurance Agreements, Asset Fair Value Disclosure	60	[1]	56	[2]
Cash and cash equivalents	3,547	[1]	2,055	[2]
Short-term investments	463	[1]	313	[2]
Derivative Assets (Liabilities), at Fair Value, Net	119	[1]	121	[2]
Investments, Fair Value Disclosure	137	[1]	138	[2]
Assets, Fair Value Disclosure	90,157	[1]	80,121	[2]
Liabilities Fair Value Disclosure
Fair Value Measured On Recurring Basis Guaranteed Interest Contracts Embedded Derivatives	354		435
Funds Held under Reinsurance Agreements, Liability	(4,816)		(5,017)
Other liabilities	(478)		(486)
Financial Liabilities Fair Value Disclosure	645		761
Fair Value, Net Asset (Liability)	954		966
Derivative Liability	(187)		(160)
Derivative Asset	2		2
Fair Value Option Contractholder Directed Unit Linked Investments [Member]
Assets Fair Value Disclosure
Investments, Fair Value Disclosure	18	[1]	17	[2]
Corporate Debt Securities [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	57,326	[1]	50,991	[2]
Canadian and Canadian provincial governments
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	5,134	[1]	5,016	[2]
Residential mortgage-backed securities
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	1,522	[1]	1,317	[2]
Asset-backed Securities [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	6,016	[1]	5,040	[2]
Assets, Fair Value Disclosure	672		564
Commercial Mortgage Backed Securities [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	2,076	[1]	2,267	[2]
US Treasury and Government [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	1,370	[1]	2,464	[2]
US States and Political Subdivisions Debt Securities [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	699	[1]	693	[2]
Debt Security, Government, Non-US [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	6,162	[1]	5,384	[2]
Japanese Government
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	5,738	[1]	4,445	[2]
Fair Value Inputs Level 1 Member
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	1,295	[1]	2,379	[2]
Equity Method Investments, Fair Value Disclosure	64	[1]	67	[2]
Funds withheld at interest embedded derivatives	0	[1]	0	[2]
Funds Held Under Reinsurance Agreements, Asset Fair Value Disclosure	0	[1]	0	[2]
Cash and cash equivalents	3,494	[1]	2,053	[2]
Short-term investments	393	[1]	175	[2]
Derivative Assets (Liabilities), at Fair Value, Net	0	[1]	0	[2]
Investments, Fair Value Disclosure	0	[1]	0	[2]
Assets, Fair Value Disclosure	5,246	[1]	4,674	[2]
Liabilities Fair Value Disclosure
Fair Value Measured On Recurring Basis Guaranteed Interest Contracts Embedded Derivatives	0		0
Other liabilities	0		0
Financial Liabilities Fair Value Disclosure	0		0
Derivative Liability	0		0
Derivative Asset	0		0
Fair Value Inputs Level 1 Member | Fair Value Option Contractholder Directed Unit Linked Investments [Member]
Assets Fair Value Disclosure
Investments, Fair Value Disclosure	0	[1]	0	[2]
Fair Value Inputs Level 1 Member | Corporate Debt Securities [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	0	[1]	0	[2]
Fair Value Inputs Level 1 Member | Canadian and Canadian provincial governments
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	0	[1]	0	[2]
Fair Value Inputs Level 1 Member | Residential mortgage-backed securities
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	0	[1]	0	[2]
Fair Value Inputs Level 1 Member | Asset-backed Securities [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	0	[1]	0	[2]
Fair Value Inputs Level 1 Member | Commercial Mortgage Backed Securities [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	0	[1]	0	[2]
Fair Value Inputs Level 1 Member | US Treasury and Government [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	1,295	[1]	2,379	[2]
Fair Value Inputs Level 1 Member | US States and Political Subdivisions Debt Securities [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	0	[1]	0	[2]
Fair Value Inputs Level 1 Member | Debt Security, Government, Non-US [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	0	[1]	0	[2]
Fair Value Inputs Level 1 Member | Japanese Government
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	0	[1]	0	[2]
Fair Value Inputs Level 2 Member
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	73,539	[1]	66,550	[2]
Equity Method Investments, Fair Value Disclosure	0	[1]	0	[2]
Funds withheld at interest embedded derivatives	0	[1]	0	[2]
Funds Held Under Reinsurance Agreements, Asset Fair Value Disclosure	0	[1]	0	[2]
Cash and cash equivalents	53	[1]	2	[2]
Short-term investments	61	[1]	127	[2]
Derivative Assets (Liabilities), at Fair Value, Net	119	[1]	121	[2]
Investments, Fair Value Disclosure	137	[1]	138	[2]
Assets, Fair Value Disclosure	73,790	[1]	66,817	[2]
Liabilities Fair Value Disclosure
Fair Value Measured On Recurring Basis Guaranteed Interest Contracts Embedded Derivatives	0		0
Other liabilities	(476)		(484)
Financial Liabilities Fair Value Disclosure	476		484
Derivative Liability	0		0
Derivative Asset	0		0
Fair Value Inputs Level 2 Member | Fair Value Option Contractholder Directed Unit Linked Investments [Member]
Assets Fair Value Disclosure
Investments, Fair Value Disclosure	18	[1]	17	[2]
Fair Value Inputs Level 2 Member | Corporate Debt Securities [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	48,414	[1]	44,137	[2]
Fair Value Inputs Level 2 Member | Canadian and Canadian provincial governments
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	5,134	[1]	5,016	[2]
Fair Value Inputs Level 2 Member | Residential mortgage-backed securities
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	3,779	[1]	1,317	[2]
Fair Value Inputs Level 2 Member | Asset-backed Securities [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	2,052	[1]	3,254	[2]
Fair Value Inputs Level 2 Member | Commercial Mortgage Backed Securities [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	1,522	[1]	2,254	[2]
Fair Value Inputs Level 2 Member | US Treasury and Government [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	71	[1]	80	[2]
Fair Value Inputs Level 2 Member | US States and Political Subdivisions Debt Securities [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	699	[1]	693	[2]
Fair Value Inputs Level 2 Member | Debt Security, Government, Non-US [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	6,130	[1]	5,354	[2]
Fair Value Inputs Level 2 Member | Japanese Government
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	5,738	[1]	4,445	[2]
Fair Value Inputs Level 3 Member
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	11,209	[1]	8,688	[2]
Equity Method Investments, Fair Value Disclosure	91	[1]	88	[2]
Funds withheld at interest embedded derivatives	(250)	[1]	(215)	[2]
Funds Held Under Reinsurance Agreements, Asset Fair Value Disclosure	60	[1]	56	[2]
Cash and cash equivalents	0	[1]	0	[2]
Short-term investments	9	[1]	11	[2]
Derivative Assets (Liabilities), at Fair Value, Net	0	[1]	0	[2]
Investments, Fair Value Disclosure	0	[1]	0	[2]
Assets, Fair Value Disclosure	11,121	[1]	8,630	[2]
Liabilities Fair Value Disclosure
Fair Value Measured On Recurring Basis Guaranteed Interest Contracts Embedded Derivatives	354		435
Other liabilities	(2)		(2)
Financial Liabilities Fair Value Disclosure	169		277
Derivative Liability	(187)		(160)
Derivative Asset	2		2
Fair Value Inputs Level 3 Member | Fair Value Option Contractholder Directed Unit Linked Investments [Member]
Assets Fair Value Disclosure
Investments, Fair Value Disclosure	0	[1]	0	[2]
Fair Value Inputs Level 3 Member | Corporate Debt Securities [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	8,912	[1]	6,854	[2]
Fair Value Inputs Level 3 Member | Canadian and Canadian provincial governments
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	0	[1]	0	[2]
Fair Value Inputs Level 3 Member | Residential mortgage-backed securities
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	2,237	[1]	0	[2]
Fair Value Inputs Level 3 Member | Asset-backed Securities [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	24	[1]	1,786	[2]
Fair Value Inputs Level 3 Member | Commercial Mortgage Backed Securities [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	0	[1]	13	[2]
Fair Value Inputs Level 3 Member | US Treasury and Government [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	4	[1]	5	[2]
Fair Value Inputs Level 3 Member | US States and Political Subdivisions Debt Securities [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	0	[1]	0	[2]
Fair Value Inputs Level 3 Member | Debt Security, Government, Non-US [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	32	[1]	30	[2]
Fair Value Inputs Level 3 Member | Japanese Government
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	$ 0	[1]	$ 0	[2]

[1] Excludes limited partnerships that are measured at estimated fair value using the NAV per share (or its equivalent) as a practical expedient. As of June 30, 2025, the fair value of such investments was $954 million.

[2] Excludes limited partnerships that are measured at estimated fair value using the NAV per share (or its equivalent) as a practical expedient. As of December 31, 2024, the fair value of such investments was $966 million