Condensed Financial Information of Parent Company - Condensed Statement of Earnings (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues:
Total revenues	$ 1,808	$ 1,835	$ 1,646	$ 1,576	$ 1,737	$ 1,705	$ 1,581	$ 1,475	$ 6,865	$ 6,498	$ 6,145
Costs and Expenses:
Other expenses									422	353	336
Total costs and expenses									6,141	5,711	5,580
Earnings before income taxes									724	787	565
Provision for income taxes									247	119	195
Net Earnings Attributable to Shareholders	166	$ 11	$ 145	$ 153	385	$ 109	$ 54	$ 101	475	649	352
AFG
Revenues:
Dividends from subsidiaries									681	643	311
Equity in undistributed earnings of subsidiaries									264	286	386
Investment and other income									13	7	4
Total revenues									958	936	701
Costs and Expenses:
Interest charges on intercompany borrowings									9	9	9
Interest charges on other borrowings									85	77	73
Other expenses									142	82	72
Total costs and expenses									236	168	154
Earnings before income taxes									722	768	547
Provision for income taxes	$ (56)				$ (177)				247	119	195
Net Earnings Attributable to Shareholders									$ 475	$ 649	$ 352