Income Taxes - Reconciliation of income taxes at the statutory rate to the provision for income taxes (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Earnings before income taxes (“EBT”)	$ 205	$ 136	$ 428	$ 292
Income taxes at statutory rate	72	47	150	102
Effect of stock-based compensation	(7)	0	(13)	0
Effect of tax exempt interest	(6)	(6)	(12)	(13)
Effect of dividends received deduction	(2)	(2)	(4)	(4)
Effect of employee stock ownership plan dividends paid deduction	(2)	0	(2)	(1)
Effect of change in valuation allowance	2	32	0	33
Effect of subsidiaries not in AFG's tax return	0	1	0	2
Effect of other income tax reconciliation	3	1	9	6
Provision for income taxes as shown on the Statement of Earnings	$ 60	$ 73	$ 128	$ 125
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Income taxes at statutory rate as a percentage of EBT	35.00%	35.00%	35.00%	35.00%
Effect of stock-based compensation as a percentage of EBT	(3.00%)	0.00%	(3.00%)	0.00%
Effect of tax exempt interest as a percentage of EBT	(3.00%)	(4.00%)	(3.00%)	(4.00%)
Effect of dividends received deduction as a percentage of EBT	(1.00%)	(1.00%)	(1.00%)	(1.00%)
Effect of employee stock ownership plan dividends paid deduction as a percentage of EBT	(1.00%)	(0.00%)	(0.00%)	(0.00%)
Effect of change in valuation allowance as a percentage of EBT	1.00%	24.00%	0.00%	11.00%
Effect of subsidiaries not in AFG's tax return as a percentage of EBT	0.00%	1.00%	0.00%	1.00%
Effect of other income tax reconciliation as a percentage of EBT	1.00%	(1.00%)	2.00%	1.00%
Provision for income taxes as shown on the Statement of Earnings as a percentage of EBT	29.00%	54.00%	30.00%	43.00%