Financing - Schedule of Variable Stock Purchase Contract Settlement Rates (Parenthetical) (Details)	1 Months Ended
Feb. 28, 2021 Day
Spire \| 2021 Series A 0.75% Remarketable Senior Notes
Equity Units [Line Items]
Trading days before settlement	20

Threshold number of specified trading days that common stock price to conversion price of convertible debt instruments must exceed threshold percentage within a specified consecutive trading period to trigger conversion feature.

No definition available.

Name:	us-gaap_DebtInstrumentConvertibleThresholdTradingDays
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration