Investments (Investments in Fixed Maturity and Equity Securities Available-for-Sale by Sector) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Financing Receivable, Allowance for Credit Loss	$ 33
Fixed Maturities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	46,620	$ 46,753
Financing Receivable, Allowance for Credit Loss	33	0
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	3,429	4,478
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	1,461	110
Estimated Fair Value	$ 48,555	$ 51,121
% of Total	100.00%	100.00%
Other-than-temporary impairments in AOCI		$ 0
Corporate Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 29,203	29,205
Estimated Fair Value	$ 29,494	$ 31,393
% of Total	100.00%	100.00%
Corporate Debt Securities [Member] \| Fixed Maturities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 29,203	$ 29,205
Financing Receivable, Allowance for Credit Loss	26	0
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	1,294	2,269
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	977	81
Estimated Fair Value	$ 29,494	$ 31,393
% of Total	60.80%	61.40%
Other-than-temporary impairments in AOCI		$ 0
Canadian and Canadian provincial governments \| Fixed Maturities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 2,793	3,016
Financing Receivable, Allowance for Credit Loss	0
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	1,445	1,596
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	1	0
Estimated Fair Value	$ 4,237	$ 4,612
% of Total	8.70%	9.00%
Other-than-temporary impairments in AOCI		$ 0
Residential mortgage-backed securities \| Fixed Maturities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 2,241	2,339
Financing Receivable, Allowance for Credit Loss	0
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	77	62
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	27	3
Estimated Fair Value	$ 2,291	$ 2,398
% of Total	4.70%	4.70%
Other-than-temporary impairments in AOCI		$ 0
Asset-backed Securities [Member] \| Fixed Maturities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 2,940	2,973
Financing Receivable, Allowance for Credit Loss	0
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	4	19
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	277	14
Estimated Fair Value	$ 2,667	$ 2,978
% of Total	5.50%	5.80%
Other-than-temporary impairments in AOCI		$ 0
Commercial Mortgage Backed Securities [Member] \| Fixed Maturities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 1,841	1,841
Financing Receivable, Allowance for Credit Loss	0
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	24	61
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	56	3
Estimated Fair Value	$ 1,809	$ 1,899
% of Total	3.70%	3.70%
Other-than-temporary impairments in AOCI		$ 0
US Treasury and Government [Member] \| Fixed Maturities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 1,398	2,096
Financing Receivable, Allowance for Credit Loss	0
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	244	57
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0	1
Estimated Fair Value	$ 1,642	$ 2,152
% of Total	3.40%	4.20%
Other-than-temporary impairments in AOCI		$ 0
US States and Political Subdivisions Debt Securities [Member] \| Fixed Maturities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 1,071	1,074
Financing Receivable, Allowance for Credit Loss	0
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	108	93
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	10	3
Estimated Fair Value	$ 1,169	$ 1,164
% of Total	2.40%	2.30%
Other-than-temporary impairments in AOCI		$ 0
Debt Security, Government, Non-US [Member] \| Fixed Maturities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 5,133	4,209
Financing Receivable, Allowance for Credit Loss	7	0
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	233	321
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	113	5
Estimated Fair Value	$ 5,246	$ 4,525
% of Total	10.80%	8.90%
Other-than-temporary impairments in AOCI		$ 0

Percentage of available for sale securities

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Accumulated other comprehensive loss related to portion of other than temporary impairment (OTTI) due to factors other than credit losses on debt securities categorized as available-for-sale that an entity does not intend to sell and which it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis of the debt security. The amount represented by this item is net of tax, as applicable.

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Amount of allowance for credit loss on financing receivable. Excludes allowance for financing receivable covered under loss sharing agreement.

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