Fair Value of Assets and Liabilities (Balances of Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	$ 54,652	$ 51,121
Equity Method Investments, Fair Value Disclosure	135	320
Funds withheld at interest embedded derivatives	7	121
Cash and cash equivalents	1,835	274
Short-term investments	101	32
Derivative Assets (Liabilities), at Fair Value, Net		117
Investments, Fair Value Disclosure	436	377
Assets, Fair Value Disclosure	57,166	52,245
Fair Value Measured On Recurring Basis Guaranteed Interest Contracts Embedded Derivatives	980	930
Liabilities Fair Value Disclosure
Other liabilities		(53)
Financial Liabilities Fair Value Disclosure	1,038	983
Other
Assets Fair Value Disclosure
Investments, Fair Value Disclosure	4	0
Interest Rate Swap [Member]
Assets Fair Value Disclosure
Investments, Fair Value Disclosure	174
Liabilities Fair Value Disclosure
Other liabilities	(58)
Fair Value Option Contractholder Directed Unit Linked Investments [Member]
Assets Fair Value Disclosure
Investments, Fair Value Disclosure	258	260
Corporate Debt Securities [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	34,259	31,393
Canadian and Canadian provincial governments
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	4,897	4,612
Residential mortgage-backed securities
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	2,027	2,398
Asset-backed securities
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	2,922	2,978
Assets, Fair Value Disclosure	80	101
Commercial Mortgage Backed Securities [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	1,930	1,899
US Government Agencies Debt Securities [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	1,630	2,152
Assets, Fair Value Disclosure	15	16
US States and Political Subdivisions Debt Securities [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	1,383	1,164
Debt Security, Government, Non-US [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	5,604	4,525
Fair Value Inputs Level 1 Member
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	1,520	2,030
Equity Method Investments, Fair Value Disclosure	75	243
Funds withheld at interest embedded derivatives	0	0
Cash and cash equivalents	1,825	274
Short-term investments	20	4
Derivative Assets (Liabilities), at Fair Value, Net		0
Investments, Fair Value Disclosure	201	207
Assets, Fair Value Disclosure	3,641	2,758
Fair Value Measured On Recurring Basis Guaranteed Interest Contracts Embedded Derivatives	0	0
Liabilities Fair Value Disclosure
Other liabilities		0
Financial Liabilities Fair Value Disclosure	0	0
Fair Value Inputs Level 1 Member | Other
Assets Fair Value Disclosure
Investments, Fair Value Disclosure	0	0
Fair Value Inputs Level 1 Member | Interest Rate Swap [Member]
Assets Fair Value Disclosure
Investments, Fair Value Disclosure	0
Liabilities Fair Value Disclosure
Other liabilities	0
Fair Value Inputs Level 1 Member | Fair Value Option Contractholder Directed Unit Linked Investments [Member]
Assets Fair Value Disclosure
Investments, Fair Value Disclosure	201	207
Fair Value Inputs Level 1 Member | Corporate Debt Securities [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	0	0
Fair Value Inputs Level 1 Member | Canadian and Canadian provincial governments
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	0	0
Fair Value Inputs Level 1 Member | Residential mortgage-backed securities
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	0	0
Fair Value Inputs Level 1 Member | Asset-backed securities
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	0	0
Fair Value Inputs Level 1 Member | Commercial Mortgage Backed Securities [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	0	0
Fair Value Inputs Level 1 Member | US Government Agencies Debt Securities [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	1,520	2,030
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	0
Fair Value Inputs Level 1 Member | Debt Security, Government, Non-US [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	0	0
Fair Value Inputs Level 2 Member
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	50,358	45,952
Equity Method Investments, Fair Value Disclosure	0	0
Funds withheld at interest embedded derivatives	0	0
Cash and cash equivalents	10	0
Short-term investments	75	26
Derivative Assets (Liabilities), at Fair Value, Net		117
Investments, Fair Value Disclosure	235	170
Assets, Fair Value Disclosure	50,678	46,148
Fair Value Measured On Recurring Basis Guaranteed Interest Contracts Embedded Derivatives	0	0
Liabilities Fair Value Disclosure
Other liabilities		(53)
Financial Liabilities Fair Value Disclosure	58	53
Fair Value Inputs Level 2 Member | Other
Assets Fair Value Disclosure
Investments, Fair Value Disclosure	4	0
Fair Value Inputs Level 2 Member | Interest Rate Swap [Member]
Assets Fair Value Disclosure
Investments, Fair Value Disclosure	174
Liabilities Fair Value Disclosure
Other liabilities	(58)
Fair Value Inputs Level 2 Member | Fair Value Option Contractholder Directed Unit Linked Investments [Member]
Assets Fair Value Disclosure
Investments, Fair Value Disclosure	57	53
Fair Value Inputs Level 2 Member | Corporate Debt Securities [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	31,732	29,207
Fair Value Inputs Level 2 Member | Canadian and Canadian provincial governments
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	4,897	3,908
Fair Value Inputs Level 2 Member | Residential mortgage-backed securities
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	2,023	2,349
Fair Value Inputs Level 2 Member | Asset-backed securities
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	2,772	2,865
Fair Value Inputs Level 2 Member | Commercial Mortgage Backed Securities [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	1,878	1,853
Fair Value Inputs Level 2 Member | US Government Agencies Debt Securities [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	95	106
Fair Value Inputs Level 2 Member | US States and Political Subdivisions Debt Securities [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	1,374	1,155
Fair Value Inputs Level 2 Member | Debt Security, Government, Non-US [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	5,587	4,509
Fair Value Inputs Level 3 Member
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	2,774	3,139
Equity Method Investments, Fair Value Disclosure	60	77
Funds withheld at interest embedded derivatives	7	121
Cash and cash equivalents	0	0
Short-term investments	6	2
Derivative Assets (Liabilities), at Fair Value, Net		0
Investments, Fair Value Disclosure	0	0
Assets, Fair Value Disclosure	2,847	3,339
Fair Value Measured On Recurring Basis Guaranteed Interest Contracts Embedded Derivatives	980	930
Liabilities Fair Value Disclosure
Other liabilities		0
Financial Liabilities Fair Value Disclosure	980	930
Fair Value Inputs Level 3 Member | Other
Assets Fair Value Disclosure
Investments, Fair Value Disclosure	0	0
Fair Value Inputs Level 3 Member | Interest Rate Swap [Member]
Assets Fair Value Disclosure
Investments, Fair Value Disclosure	0
Liabilities Fair Value Disclosure
Other liabilities	0
Fair Value Inputs Level 3 Member | Fair Value Option Contractholder Directed Unit Linked Investments [Member]
Assets Fair Value Disclosure
Investments, Fair Value Disclosure	0	0
Fair Value Inputs Level 3 Member | Corporate Debt Securities [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	2,527	2,186
Fair Value Inputs Level 3 Member | Canadian and Canadian provincial governments
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	0	704
Fair Value Inputs Level 3 Member | Residential mortgage-backed securities
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	4	49
Fair Value Inputs Level 3 Member | Asset-backed securities
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	150	113
Fair Value Inputs Level 3 Member | Commercial Mortgage Backed Securities [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	52	46
Fair Value Inputs Level 3 Member | US Government Agencies Debt Securities [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	15	16
Fair Value Inputs Level 3 Member | US States and Political Subdivisions Debt Securities [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	9	9
Fair Value Inputs Level 3 Member | Debt Security, Government, Non-US [Member]
Assets Fair Value Disclosure
Fixed maturity securities, available-for-sale	$ 17	$ 16