Schedule 2 - Parent Company Financial Statements - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Jul. 02, 2018
5.0% Senior Notes due September 19, 2022 | Senior Notes
Condensed Financial Statements, Captions [Line Items]
Stated interest rate, percentage	5.00%
5.0% Senior Notes due September 19, 2022 | Senior Notes | Infinity Property and Casualty Corporation
Condensed Financial Statements, Captions [Line Items]
Stated interest rate, percentage			5.00%
Subsidiary of Common Parent | Non-cash Dividends
Condensed Financial Statements, Captions [Line Items]
Related party transaction, amounts of transaction	$ 0	$ 574,000,000
Subsidiary of Common Parent | Non-cash Capital Contributions
Condensed Financial Statements, Captions [Line Items]
Related party transaction, amounts of transaction	$ 0	$ 350,000,000