Fair Value Measurements (Changes in Level 3 Liabilities) (Details) - SWAPS RELATED TO SALE OF CERTAIN VISA CLASS B COMMON SHARES - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value liabilities beginning balance	$ 34.6	$ 26.5	$ 35.3	$ 33.4
Total (Gains) Losses:
Included in Earnings	8.5	8.6	12.1	5.7
Purchases, Issues, Sales, and Settlements
Settlements	(4.7)	(3.8)	(9.0)	(7.8)
Fair value liabilities ending balance	$ 38.4	$ 31.3	$ 38.4	$ 31.3

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

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- Definition

Amount of gain (loss) recognized in income from liability measured at fair value on recurring basis using unobservable input (level 3).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=123874694&loc=d3e19207-110258

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Amount of settlements of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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-Section 50
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- Definition

Fair value of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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-Section 50
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