Pledged and Restricted Assets (Accepted Collateral) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Reverse repurchase agreements
Financial Instruments Owned and Pledged as Collateral [Line Items]
Collateral that may be repledged or sold	$ 309.3	$ 1,179.8
Collateral that may not be repledged or sold	800.0	500.0
Derivative contracts
Financial Instruments Owned and Pledged as Collateral [Line Items]
Collateral that may be repledged or sold	$ 8.4	$ 0.9

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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
-Paragraph 1A
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=109249958&loc=SL6224234-111729

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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.

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- Definition

The carrying amount (fair value) as of the balance sheet date of securities held that had been pledged by counterparties under financing and lending arrangements, pursuant to which the entity has the right by agreement or custom to sell or re-pledge such securities.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=121611835&loc=d3e5086-111524

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