Investments (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Investment [Line Items]
Average remaining maturities for short-term available for sale investments, in months	4 months
Average remaining maturities for long-term available for sale investments, in years	2 years
Realized gains on the sales of available-for-sale investments	$ 1.5	$ 0.1
Realized losses on the sales of available-for-sale investments	0.9	1.5
Other-than-temporary impairment, available-for-sale securities		4.6
Gross realized losses on available-for-sale securities not deemed other-than-temporary	0.1	2.9
Unfunded commitments	0.7
Significant Unobservable Inputs (Level 3)
Investment [Line Items]
Downward adjustment to direct investments in privately-held companies	0.0	0.0
Upward adjustment to direct investments in privately-held companies	0.0	0.0
Private Equity Funds
Investment [Line Items]
Alternative Investment	11.2	10.9
Other Assets
Investment [Line Items]
Direct investments in privately-held companies	$ 12.3	$ 13.4

Represents the average remaining maturities for long-term available for sale investments, in years.

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The average remaining maturity period for short-term available-for-sale investments, in PnM format

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Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, not OTTI, before Tax

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- Definition

Amount of investment in equity security without readily determinable fair value.

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- Definition

Fair value of investment other than investment in equity security, investment in debt security and equity method investment. Includes, but is not limited to, investment in certain entities that calculate net asset value per share. Example includes, but is not limited to, investment in hedge fund, venture capital fund, private equity fund, and real estate partnership or fund.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Amount of realized gain on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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Amount of realized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of loss from downward price adjustment on investment in equity security without readily determinable fair value.

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Amount of gain from upward price adjustment on investment in equity security without readily determinable fair value.

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- Definition

The amount of unfunded commitments for which the entity is obligated, to those certain investments for which net asset value per share is calculated (including by unit, membership interest, or other equity (ownership interest) unit measure) (alternative investments).

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Amount of other-than-temporary impairment (OTTI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), recognized in earnings and other comprehensive loss (OCI).

+ References

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