Financial Risk Management - Market Price Fluctuations - Pre Tax Foreign Exchange (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Disclosure of nature and extent of risks arising from financial instruments [abstract]
Investing activities	$ (68.0)	$ (171.3)
Underwriting activities	5.6	31.6
Foreign currency forward contracts	(1.3)	7.9
Foreign currency net gains (losses) included in pre-tax earnings (loss)	$ (63.7)	$ (131.8)

Amount before tax of foreign currency transaction realized and unrealized gain (loss) recognized in the income statement.

No definition available.

Name:	ffh_ForeignCurrencyTransactionGainLossBeforeTax1
Namespace Prefix:	ffh_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration