Pledged and Restricted Assets - Fair Value of Available for Sale Debt Securities Included In Pledged Assets (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Financial Instruments Owned and Pledged as Collateral [Line Items]
Amount of securities and loans pledged	$ 42,100.0	$ 39,600.0
Securities Available for Sale
Financial Instruments Owned and Pledged as Collateral [Line Items]
Amount of securities and loans pledged	487.1	151.5
Repurchase agreements
Financial Instruments Owned and Pledged as Collateral [Line Items]
Amount of securities and loans pledged	$ 14.4	$ 29.0

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.

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 (b)(1)(i)
-URI http://asc.fasb.org/extlink&oid=109249958&loc=SL6224234-111729

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-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

Name:	us-gaap_SecurityOwnedAndPledgedAsCollateralFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant