Investments (Investments Pledged as Collateral) (Details) $ in Millions	3 Months Ended
Mar. 31, 2018 USD ($)
Financial Instruments Owned and Pledged as Collateral [Line Items]
Increase in Pledged Collateral	$ 82.3
Carrying Value Bonds On Deposit With Various State And Regulatory Agencies	25.4
Securities Pledged As Collateral	249.3
U.S. Government and Government Agencies [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Carrying Value Bonds On Deposit With Various State And Regulatory Agencies	22.2
Securities Pledged As Collateral	25.2
Obligations of States and Political Subdivisions [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Carrying Value Bonds On Deposit With Various State And Regulatory Agencies	3.2
Securities Pledged As Collateral	3.2
Commercial Mortgage Backed Securities [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Carrying Value Bonds On Deposit With Various State And Regulatory Agencies	0.0
Securities Pledged As Collateral	30.8
Residential Mortgage Backed Securities [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Carrying Value Bonds On Deposit With Various State And Regulatory Agencies	0.0
Securities Pledged As Collateral	190.1
Federal Home Loan Bank of Indianapolis [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Fixed Income Securities Pledged For FHLB Collateral	67.9
Federal Home Loan Bank of Indianapolis [Member] \| U.S. Government and Government Agencies [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Fixed Income Securities Pledged For FHLB Collateral	3.0
Federal Home Loan Bank of Indianapolis [Member] \| Obligations of States and Political Subdivisions [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Fixed Income Securities Pledged For FHLB Collateral	0.0
Federal Home Loan Bank of Indianapolis [Member] \| Commercial Mortgage Backed Securities [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Fixed Income Securities Pledged For FHLB Collateral	7.3
Federal Home Loan Bank of Indianapolis [Member] \| Residential Mortgage Backed Securities [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Fixed Income Securities Pledged For FHLB Collateral	57.6
Federal Home Loan Bank of New York [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Fixed Income Securities Pledged For FHLB Collateral	156.0
Federal Home Loan Bank of New York [Member] \| U.S. Government and Government Agencies [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Fixed Income Securities Pledged For FHLB Collateral	0.0
Federal Home Loan Bank of New York [Member] \| Obligations of States and Political Subdivisions [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Fixed Income Securities Pledged For FHLB Collateral	0.0
Federal Home Loan Bank of New York [Member] \| Commercial Mortgage Backed Securities [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Fixed Income Securities Pledged For FHLB Collateral	23.5
Federal Home Loan Bank of New York [Member] \| Residential Mortgage Backed Securities [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Fixed Income Securities Pledged For FHLB Collateral	$ 132.5

Increase or decrease during the period in FHLBNY securities pledged as collateral.

No definition available.

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- Definition

Carrying amount of cash and investment securities on deposit with state regulatory authorities in connection with capital requirements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 320
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=75027294&loc=d3e22002-158495

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- Definition

Amount of the collateral pledged in support of federal home loan bank advances outstanding.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6479118&loc=d3e64650-112822

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=75038535&loc=d3e64711-112823

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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.

+ References

No definition available.

+ Details

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- Definition

Fair value of financial instrument held by the entity for its own account (proprietary securities) for trading or investment purposes that are carried at fair value and pledged to counterparties as collateral for financing transactions.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
-Paragraph 1A
-Subparagraph (b)(1)(i)
-URI http://asc.fasb.org/extlink&oid=64858031&loc=SL6224234-111729

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=66007379&loc=d3e113888-111728

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