Investments (Investments in Fixed Maturity and Equity Securities Available-for-Sale by Sector) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Amortized Cost Basis	$ 31,963	$ 29,205
Available-for-sale Securities	36,208	31,393
Financing Receivable, Allowance for Credit Loss	20
Fixed Maturities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Amortized Cost Basis	49,548	46,753
Available-for-sale Securities, Gross Unrealized Gains	7,404	4,478
Available-for-sale Securities, Gross Unrealized Losses	197	110
Available-for-sale Securities	$ 56,735	$ 51,121
Percentage Of Total Available For Sale Securities	100.00%	100.00%
Financing Receivable, Allowance for Credit Loss	$ 20
Corporate Debt Securities [Member] \| Fixed Maturities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Amortized Cost Basis	31,963	$ 29,205
Available-for-sale Securities, Gross Unrealized Gains	4,356	2,269
Available-for-sale Securities, Gross Unrealized Losses	94	81
Available-for-sale Securities	$ 36,208	$ 31,393
Percentage Of Total Available For Sale Securities	63.90%	61.40%
Financing Receivable, Allowance for Credit Loss	$ 17
Canadian Provincial Governments [Member] \| Fixed Maturities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Amortized Cost Basis	3,145	$ 3,016
Available-for-sale Securities, Gross Unrealized Gains	1,995	1,596
Available-for-sale Securities, Gross Unrealized Losses	0	0
Available-for-sale Securities	$ 5,140	$ 4,612
Percentage Of Total Available For Sale Securities	9.10%	9.00%
Financing Receivable, Allowance for Credit Loss	$ 0
Residential Mortgage Backed Securities [Member] \| Fixed Maturities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Amortized Cost Basis	1,735	$ 2,339
Available-for-sale Securities, Gross Unrealized Gains	84	62
Available-for-sale Securities, Gross Unrealized Losses	2	3
Available-for-sale Securities	$ 1,817	$ 2,398
Percentage Of Total Available For Sale Securities	3.20%	4.70%
Financing Receivable, Allowance for Credit Loss	$ 0
Asset-backed Securities [Member] \| Fixed Maturities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Amortized Cost Basis	3,099	$ 2,973
Available-for-sale Securities, Gross Unrealized Gains	35	19
Available-for-sale Securities, Gross Unrealized Losses	42	14
Available-for-sale Securities	$ 3,092	$ 2,978
Percentage Of Total Available For Sale Securities	5.40%	5.80%
Financing Receivable, Allowance for Credit Loss	$ 0
Commercial Mortgage Backed Securities [Member] \| Fixed Maturities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Amortized Cost Basis	1,790	$ 1,841
Available-for-sale Securities, Gross Unrealized Gains	102	61
Available-for-sale Securities, Gross Unrealized Losses	21	3
Available-for-sale Securities	$ 1,868	$ 1,899
Percentage Of Total Available For Sale Securities	3.30%	3.70%
Financing Receivable, Allowance for Credit Loss	$ 3
US Treasury and Government [Member] \| Fixed Maturities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Amortized Cost Basis	1,242	$ 2,096
Available-for-sale Securities, Gross Unrealized Gains	196	57
Available-for-sale Securities, Gross Unrealized Losses	1	1
Available-for-sale Securities	$ 1,437	$ 2,152
Percentage Of Total Available For Sale Securities	2.50%	4.20%
Financing Receivable, Allowance for Credit Loss	$ 0
US States and Political Subdivisions Debt Securities [Member] \| Fixed Maturities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Amortized Cost Basis	1,237	$ 1,074
Available-for-sale Securities, Gross Unrealized Gains	157	93
Available-for-sale Securities, Gross Unrealized Losses	4	3
Available-for-sale Securities	$ 1,390	$ 1,164
Percentage Of Total Available For Sale Securities	2.40%	2.30%
Financing Receivable, Allowance for Credit Loss	$ 0
Debt Security, Government, Non-US [Member] \| Fixed Maturities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Amortized Cost Basis	5,337	$ 4,209
Available-for-sale Securities, Gross Unrealized Gains	479	321
Available-for-sale Securities, Gross Unrealized Losses	33	5
Available-for-sale Securities	$ 5,783	$ 4,525
Percentage Of Total Available For Sale Securities	10.20%	8.90%
Financing Receivable, Allowance for Credit Loss	$ 0

Percentage of available for sale securities

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

+ References

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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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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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.

+ References

No definition available.

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This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References

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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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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

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