Income Taxes - Reconciliation of income taxes at the statutory rate to the provision for income taxes (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Earnings before income taxes (“EBT”)	$ 223	$ 156
Income taxes at statutory rate	78	55
Effect of tax exempt interest	(6)	(7)
Effect of stock-based compensation	(6)	0
Effect of change in valuation allowance	(2)	1
Effect of subsidiaries not in AFG's tax return	0	1
Effect of other income tax reconciliation	4	2
Provision for income taxes as shown on the Statement of Earnings	$ 68	$ 52
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Income taxes at statutory rate as a percentage of EBT	35.00%	35.00%
Effect of tax exempt interest as a percentage of EBT	(3.00%)	(4.00%)
Effect of stock-based compensation as a percentage of EBT	(3.00%)	0.00%
Effect of change in valuation allowance as a percentage of EBT	(1.00%)	1.00%
Effect of subsidiaries not in AFG's tax return as a percentage of EBT	0.00%	0.00%
Effect of other income tax reconciliation as a percentage of EBT	2.00%	1.00%
Provision for income taxes as shown on the Statement of Earnings as a percentage of EBT	30.00%	33.00%