Fair Value of Assets and Liabilities Fair Value of Assets and Liabilities (Balances of Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) - USD ($) $ in Millions	Mar. 31, 2024		Dec. 31, 2023
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	$ 65,827	[1]	$ 60,467	[2]
Equity Method Investments, Fair Value Disclosure	144	[1]	139	[2]
Funds withheld at interest embedded derivatives	(284)	[1]	(377)	[2]
Funds Held Under Reinsurance Agreements, Asset Fair Value Disclosure	55	[1]	54	[2]
Cash and cash equivalents	2,698	[1]	1,335	[2]
Short-term investments	280	[1]	187	[2]
Derivative Assets (Liabilities), at Fair Value, Net	70	[1]	97	[2]
Investments, Fair Value Disclosure	90	[1]	119	[2]
Assets, Fair Value Disclosure	68,810	[1]	61,924	[2]
Liabilities Fair Value Disclosure
Fair Value Measured On Recurring Basis Guaranteed Interest Contracts Embedded Derivatives	398		415
Derivative Liability	190		206
Funds Held under Reinsurance Agreements, Liability	(4,409)		(4,483)
Other liabilities	(294)		(197)
Financial Liabilities Fair Value Disclosure	502		406
Fair Value, Net Asset (Liability)	893		856
Fair Value Option Contractholder Directed Unit Linked Investments [Member]
Assets Fair Value Disclosure
Investments, Fair Value Disclosure	20	[1]	22	[2]
Corporate Debt Securities [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	41,048	[1]	38,755	[2]
Canadian and Canadian provincial governments
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	3,713	[1]	3,917	[2]
Residential mortgage-backed securities
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	1,150	[1]	1,079	[2]
Asset-backed Securities [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	4,945	[1]	4,429	[2]
Assets, Fair Value Disclosure	292		268
Commercial Mortgage Backed Securities [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	1,861	[1]	1,773	[2]
US Treasury and Government [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	2,786	[1]	2,520	[2]
US States and Political Subdivisions Debt Securities [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	1,116	[1]	1,114	[2]
Debt Security, Government, Non-US [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	4,004	[1]	3,749	[2]
Japanese Government
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	5,204	[1]	3,131	[2]
Fair Value Inputs Level 1 Member
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	2,694	[1]	2,426	[2]
Equity Method Investments, Fair Value Disclosure	75	[1]	69	[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	2,698	[1]	1,322	[2]
Short-term investments	178	[1]	90	[2]
Derivative Assets (Liabilities), at Fair Value, Net	0	[1]	0	[2]
Investments, Fair Value Disclosure	0	[1]	0	[2]
Assets, Fair Value Disclosure	5,645	[1]	3,907	[2]
Liabilities Fair Value Disclosure
Fair Value Measured On Recurring Basis Guaranteed Interest Contracts Embedded Derivatives	0		0
Derivative Liability	0		0
Other liabilities	0		0
Financial Liabilities Fair Value Disclosure	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	2,694	[1]	2,426	[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	56,596	[1]	51,622	[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	0	[1]	13	[2]
Short-term investments	92	[1]	95	[2]
Derivative Assets (Liabilities), at Fair Value, Net	70	[1]	97	[2]
Investments, Fair Value Disclosure	90	[1]	119	[2]
Assets, Fair Value Disclosure	56,778	[1]	51,849	[2]
Liabilities Fair Value Disclosure
Fair Value Measured On Recurring Basis Guaranteed Interest Contracts Embedded Derivatives	0		0
Derivative Liability	0		0
Other liabilities	(294)		(197)
Financial Liabilities Fair Value Disclosure	294		197
Fair Value Inputs Level 2 Member | Fair Value Option Contractholder Directed Unit Linked Investments [Member]
Assets Fair Value Disclosure
Investments, Fair Value Disclosure	20	[1]	22	[2]
Fair Value Inputs Level 2 Member | Corporate Debt Securities [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	35,969	[1]	33,822	[2]
Fair Value Inputs Level 2 Member | Canadian and Canadian provincial governments
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	3,713	[1]	3,917	[2]
Fair Value Inputs Level 2 Member | Residential mortgage-backed securities
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	1,149	[1]	1,078	[2]
Fair Value Inputs Level 2 Member | Asset-backed Securities [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	3,580	[1]	3,064	[2]
Fair Value Inputs Level 2 Member | Commercial Mortgage Backed Securities [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	1,829	[1]	1,714	[2]
Fair Value Inputs Level 2 Member | US Treasury and Government [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	86	[1]	87	[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	1,095	[1]	1,095	[2]
Fair Value Inputs Level 2 Member | Debt Security, Government, Non-US [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	3,971	[1]	3,714	[2]
Fair Value Inputs Level 2 Member | Japanese Government
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	5,204	[1]	3,131	[2]
Fair Value Inputs Level 3 Member
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	6,537	[1]	6,419	[2]
Equity Method Investments, Fair Value Disclosure	69	[1]	70	[2]
Funds withheld at interest embedded derivatives	(284)	[1]	(377)	[2]
Funds Held Under Reinsurance Agreements, Asset Fair Value Disclosure	55	[1]	54	[2]
Cash and cash equivalents	0	[1]	0	[2]
Short-term investments	10	[1]	2	[2]
Derivative Assets (Liabilities), at Fair Value, Net	0	[1]	0	[2]
Investments, Fair Value Disclosure	0	[1]	0	[2]
Assets, Fair Value Disclosure	6,387	[1]	6,168	[2]
Liabilities Fair Value Disclosure
Fair Value Measured On Recurring Basis Guaranteed Interest Contracts Embedded Derivatives	398		415
Derivative Liability	190		206
Other liabilities	0		0
Financial Liabilities Fair Value Disclosure	208		209
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	5,079	[1]	4,933	[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	1	[1]	1	[2]
Fair Value Inputs Level 3 Member | Asset-backed Securities [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	1,365	[1]	1,365	[2]
Fair Value Inputs Level 3 Member | Commercial Mortgage Backed Securities [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	32	[1]	59	[2]
Fair Value Inputs Level 3 Member | US Treasury and Government [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	6	[1]	7	[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	21	[1]	19	[2]
Fair Value Inputs Level 3 Member | Debt Security, Government, Non-US [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	33	[1]	35	[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 March 31, 2024, the fair value of such investments was $893 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, 2023, the fair value of such investments was $856 million