Investments (Narrative) (Details) $ in Millions	9 Months Ended	12 Months Ended
Sep. 30, 2019 USD ($) security item	Dec. 31, 2018 USD ($) security item
Investment [Line Items]
Increase (decrease) in gross AFS securities unrealized losses	$ (2,200)
Number of partnerships in alternative investment portfolio \| item	259	237
Alternative investments as a percentage of overall invested assets	1.00%	1.00%
Fair value of collateral received that we are permitted to sell or re-pledge	$ 178
Securities that have been re-pledged	178
Investment commitments	1,900
Investment commitments for limited partnerships	960
Investment commitments for mortgage loans on real estate	477
Investment commitments for private placements	$ 460
Commercial [Member]
Investment [Line Items]
Number of impaired loans \| security	1	0
Residential [Member]
Investment [Line Items]
Number of loans past due \| security	16
Number of impaired loans \| security	4	0
Impaired financing receivable, allowance	$ 2	$ 1
Maximum [Member] \| Commercial [Member]
Investment [Line Items]
Impaired financing receivable, carrying amount	1
Maximum [Member] \| Residential [Member]
Investment [Line Items]
Impaired financing receivable, carrying amount	1
Federal Home Loan Mortgage Corporation [Member] \| Invested Assets [Member]
Investment [Line Items]
Fair value	$ 1,300	$ 1,400
Concentration risk, percentage	1.00%	1.00%
Federal National Mortgage Association [Member] \| Invested Assets [Member]
Investment [Line Items]
Fair value	$ 1,300	$ 1,300
Concentration risk, percentage	1.00%	1.00%
Consumer Non-Cyclical Industry [Member] \| Invested Assets [Member]
Investment [Line Items]
Fair value	$ 16,000	$ 14,500
Concentration risk, percentage	12.00%	13.00%
Financial Service [Member] \| Invested Assets [Member]
Investment [Line Items]
Fair value	$ 16,300	$ 14,200
Concentration risk, percentage	12.00%	12.00%
Mortgage Loans On Real Estate [Member] \| Geographic Concentration Risk [Member] \| California [Member] \| Commercial [Member]
Investment [Line Items]
Concentration risk, percentage	24.00%	23.00%
Mortgage Loans On Real Estate [Member] \| Geographic Concentration Risk [Member] \| California [Member] \| Residential [Member]
Investment [Line Items]
Concentration risk, percentage	33.00%	34.00%
Mortgage Loans On Real Estate [Member] \| Geographic Concentration Risk [Member] \| Texas [Member] \| Commercial [Member]
Investment [Line Items]
Concentration risk, percentage	12.00%	12.00%
Mortgage Loans On Real Estate [Member] \| Geographic Concentration Risk [Member] \| Florida [Member] \| Residential [Member]
Investment [Line Items]
Concentration risk, percentage	20.00%	19.00%
Corporate Bonds [Member]
Investment [Line Items]
Percentage of fair value rated as investment grade	97.00%	96.00%
Amortized cost of portfolio rated below investment grade	$ 3,100	$ 3,200
Fair value of portfolio rated below investment grade	$ 3,100	$ 3,000
MBS [Member]
Investment [Line Items]
Severity of second lien loans	100.00%	100.00%
Severity of first lien loans	30.00%	30.00%

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Alternative investments as a percentage of overall invested assets.

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Amortized cost of portfolio rated below investment grade.

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This item represents the change in gross unrealized holding gain or loss on available-for-sale securities that has been included in accumulated other comprehensive income, a separate component of shareholders' equity, during the period.

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Percentage of the fair value of portfolio that was rated investment grade as of balance sheet date.

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Fair value of portfolio rated below investment grade.

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Financing receivable, Number of loans past due

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This item represents investment commitments as of the balance sheet date for mortgage loans.

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Number of partnerships represented in alternative investment portfolio.

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This item represents the loss severity as a percentage of first lien loans that was considered as one of the potential factors in reaching a conclusion that the available-for-sale investments are other than temporarily impaired and the amount of such impairment determined to be related to credit loss recognized in earnings.

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This item represents the loss severity as a percentage of defaulted second lien loans that was considered as one of the potential factors in reaching a conclusion that the available-for-sale investments are other than temporarily impaired and the amount of such impairment determined to be related to credit loss recognized in earnings.

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For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

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This item represents disclosure of all significant concentrations of credit risk or market risk arising from the subject financial instrument (as defined), whether from an individual counterparty or groups of counterparties.

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Fair value of collateral permitted, by contact or custom, to be sold or re-pledged.

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Fair value of the collateral, or portion thereof, that has been re-pledged, delivered, or otherwise used.

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Amount of allowance for credit losses related to recorded investment.

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Amount of investment in impaired financing receivables for which there is a related allowance for credit losses.

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