Investment Securities (Hedge Funds and Private Equity Funds) (Details) $ in Millions	3 Months Ended
Mar. 31, 2020 USD ($) fund	Dec. 31, 2019 USD ($)
Private equity security
Debt and Equity Securities, FV-NI [Line Items]
Number of investments \| fund	13
Fair Value	$ 98.5
Hedge and private equity funds included in other long-term investments
Debt and Equity Securities, FV-NI [Line Items]
Largest single fund investment	21.1	$ 54.6
Hedge funds \| Hedge funds
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	0.0	$ 54.6
Transfer from investments	$ 45.6

Value of investments transferred from the entity's investments in noncash transactions.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4313-108586

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4332-108586

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4304-108586

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration