Investments (Past Due and Interest Accrual Status of Mortgage Loans) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment, Aging [Abstract]
Past Due	$ 648	$ 511
Loans and Leases Receivable, Nonperforming, Accrual of Interest	158	144
Nonaccrual	517	367
Commercial
Financing Receivable, Recorded Investment, Aging [Abstract]
Past Due	0	3
Loans and Leases Receivable, Nonperforming, Accrual of Interest	0	3
Nonaccrual	0	0
Agricultural
Financing Receivable, Recorded Investment, Aging [Abstract]
Past Due	134	127
Loans and Leases Receivable, Nonperforming, Accrual of Interest	125	104
Nonaccrual	36	23
Residential
Financing Receivable, Recorded Investment, Aging [Abstract]
Past Due	514	381
Loans and Leases Receivable, Nonperforming, Accrual of Interest	33	37
Nonaccrual	$ 481	$ 344

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- Definition

Recorded Investment in financing receivables that are past due at the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7A
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953401-111524

+ Details

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- Definition

Reflects the carrying amount of loans deemed to be questionable as to collection on which interest is continuing to be earned or accrued.

+ References

No definition available.

+ Details

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- Definition

Reflects the carrying amount of loans deemed to be questionable as to collection on which no interest is continuing to be recognized.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5111-111524

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- Details

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