Investments (Mortgage Loans by Portfolio Segment) (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans on Real Estate, Commercial and Consumer, Net	$ 70,852	$ 68,731
Percentage Of Mortgage Loans On Real Estate To Mortgage Loans On Real Estate Commercial And Consumer Net	100.00%	100.00%
Percentage Of Loans And Leases Receivable Consumer Other To Mortgage Loans On Real Estate Commercial And Consumer Net	0.60%	0.80%
Loans Receivable, Gross, Commercial, Agricultural	$ 13,293	$ 13,014
Percentage Of Loans Receivable Commercial Agricultural To Mortgage Loans On Real Estate Commercial And Consumer Net	18.80%	18.90%
Loans Receivable, Gross, Commercial, Mortgage	$ 46,075	$ 44,375
Percentage Of Loans Receivable Commercial Mortgage To Mortgage Loans On Real Estate Commercial And Consumer Net	65.00%	64.60%
Loans and Leases Receivable, Gross, Consumer, Mortgage	$ 11,404	$ 11,136
Percentage Of Loans And Leases Receivable Consumer Mortgage To Mortgage Loans On Real Estate Commercial And Consumer Net	16.10%	16.20%
Mortgage Loans Held For Investment	$ 70,772	$ 68,525
Percentage Of Mortgage Loans Held For Investment To Mortgage Loans On Real Estate Commercial And Consumer Net	99.90%	99.70%
Allowance for Loan and Lease Losses, Real Estate	$ 325	$ 314	$ 312	$ 304
Percentage Of Allowance For Loan And Lease Losses Real Estate To Mortgage Loans On Real Estate Commercial And Consumer Net	(0.50%)	(0.50%)
Loans and Leases Receivable, Net Amount	$ 70,447	$ 68,211
Percentage Of Mortgage Loans Held For Investment Net To Mortgage Loans On Real Estate Commercial And Consumer Net	99.40%	99.20%
Residential Loans Held For Investment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans on Real Estate, Commercial and Consumer, Net	$ 405	$ 520

The balance represents the amount of loans that are secured by real estate mortgages.

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- Definition

Percentage of Allowance For Loan And Lease Losses on Real Estate to total Mortgage Loans on Real Estate.

+ References

No definition available.

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- Definition

Percentage of Consumer Mortgage Loans and Leases Receivable to total Mortgage Loans on Real Estate.

+ References

No definition available.

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- Definition

Percentage of loans and leases receivable consumer other to total mortgage loans on real estate.

+ References

No definition available.

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- Definition

Percentage of Commercial Agricultural Loans Receivable to total Mortgage Loans on Real Estate.

+ References

No definition available.

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- Definition

Percentage of Commercial Mortgage Loans Receivable to total Mortgage Loans on Real Estate.

+ References

No definition available.

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- Definition

Percentage of Mortgage Loans Held-for-investment, net to total Mortgage Loans on Real Estate.

+ References

No definition available.

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- Definition

Percentage of Mortgage Loans Held For Investment to total Mortgage Loans on Real Estate.

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No definition available.

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- Definition

Percentage of Mortgage Loans On Real Estate to total Mortgage Loans on Real Estate.

+ References

No definition available.

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- Definition

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.

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No definition available.

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- Definition

The reserve to cover probable credit losses related to specifically identified fixed maturity real estate loans as well as probable credit losses inherent in the remainder of that loan portfolio.

+ References

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- Definition

Amount before allowance of consumer mortgage. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes subordinated loans such as home equity lines of credit and loans and leases covered under loss sharing agreements.

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Amount after allowance and deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements and loans held for sale.

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- Definition

Amount before allowance of loans issued to agricultural institutions. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans covered under loss sharing agreements.

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Amount before allowance of mortgage loans on existing land or building. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans covered under loss sharing agreements.

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The balance represents the amount of loans that are secured by real estate mortgages, offset by the reserve to cover probable credit losses on the loan portfolio.

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