Shareholders' Equity - Progression of the components of accumulated other comprehensive income (Details) - USD ($) $ in Millions		3 Months Ended			9 Months Ended
		Sep. 30, 2016		Sep. 30, 2015	Sep. 30, 2016		Sep. 30, 2015
Accumulated Other Comprehensive Income [Roll Forward]
AOCI beginning balance					$ 304
Other comprehensive income (loss), net of tax		$ 85		$ (104)	456		$ (270)
AOCI ending balance		753			753
Accumulated Net Investment Gain (Loss) Including Portion Attributable to Noncontrolling Interest
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), unrealized holding gains on securities arising during the period, Pretax		138		(171)	656		(394)
Other comprehensive income (loss), unrealized holding gains on securities arising during the period, tax		(49)		61	(229)		139
Other comprehensive income (loss), unrealized holding gains on securities arising during the period, net of tax		89		(110)	427		(255)
Reclassification from accumulated other comprehensive income, pretax	[1]	(2)		16	32		(4)
Reclassification from accumulated other comprehensive income, tax	[1]	1		(6)	(12)		1
Reclassification from accumulated other comprehensive income, net of tax		(1)		10	20		(3)
Accumulated Other Comprehensive Income [Roll Forward]
Other comprehensive income (loss), pretax		136		(155)	688		(398)
Other comprehensive income (loss), tax		(48)		55	(241)		140
Other comprehensive income (loss), net of tax		88		(100)	447		(258)
Accumulated Net Investment Gain (Loss) Attributable to Noncontrolling Interest
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), unrealized holding gains on securities arising during the period, net of tax		(1)		3	(6)		5
Reclassification from accumulated other comprehensive income, net of tax	[1]	0		(1)	(1)		(1)
Accumulated Other Comprehensive Income [Roll Forward]
Other comprehensive income (loss), net of tax		(1)		2	(7)		4
Accumulated Net Investment Gain (Loss) Attributable to Parent
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), unrealized holding gains on securities arising during the period, net of tax		88		(107)	421		(250)
Reclassification from accumulated other comprehensive income, net of tax		(1)		9	19		(4)
Accumulated Other Comprehensive Income [Roll Forward]
AOCI beginning balance		685	[2]	587	332	[2]	743
Other comprehensive income (loss), net of tax		87		(98)	440		(254)
AOCI ending balance		772	[2]	489	772	[2]	489
Accumulated Net Gain (Loss) from Cash Flow Hedges Including Portion Attributable to Noncontrolling Interest
Accumulated Other Comprehensive Income [Roll Forward]
Other comprehensive income (loss), pretax		(1)		3	6		3
Other comprehensive income (loss), tax		1		(1)	(2)		(1)
Other comprehensive income (loss), net of tax		0		2	4		2
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Noncontrolling Interest
Accumulated Other Comprehensive Income [Roll Forward]
Other comprehensive income (loss), net of tax		0		0	0		0
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent
Accumulated Other Comprehensive Income [Roll Forward]
AOCI beginning balance		5		0	1		0
Other comprehensive income (loss), net of tax		0		2	4		2
AOCI ending balance		5		2	5		2
Accumulated Foreign Currency Adjustment Including Portion Attributable to Noncontrolling Interest
Accumulated Other Comprehensive Income [Roll Forward]
Other comprehensive income (loss), pretax		(2)		(5)	2		(11)
Other comprehensive income (loss), tax		(1)		(2)	2		(4)
Other comprehensive income (loss), net of tax		(3)		(7)	4		(15)
Accumulated Foreign Currency Adjustment Attributable to Noncontrolling Interest
Accumulated Other Comprehensive Income [Roll Forward]
Other comprehensive income (loss), net of tax		0		0	0		0
Accumulated Foreign Currency Adjustment Attributable to Parent
Accumulated Other Comprehensive Income [Roll Forward]
AOCI beginning balance		(15)		(16)	(22)		(8)
Other comprehensive income (loss), net of tax		(3)		(7)	4		(15)
AOCI ending balance		(18)		(23)	(18)		(23)
Accumulated Defined Benefit Plans Adjustment Including Portion Attributable to Noncontrolling Interest
Accumulated Other Comprehensive Income [Roll Forward]
Other comprehensive income (loss), pretax		0		1	1		1
Other comprehensive income (loss), tax		0		0	0		0
Other comprehensive income (loss), net of tax		0		1	1		1
Accumulated Defined Benefit Plans Adjustment Attributable to Noncontrolling Interest
Accumulated Other Comprehensive Income [Roll Forward]
Other comprehensive income (loss), net of tax		0		0	0		0
Accumulated Defined Benefit Plans Adjustment Attributable to Parent
Accumulated Other Comprehensive Income [Roll Forward]
AOCI beginning balance		(6)		(8)	(7)		(8)
Other comprehensive income (loss), net of tax		0		1	1		1
AOCI ending balance		(6)		(7)	(6)		(7)
AOCI Including Portion Attributable to Noncontrolling Interest
Accumulated Other Comprehensive Income [Roll Forward]
Other comprehensive income (loss), pretax		133		(156)	697		(405)
Other comprehensive income (loss), tax		(48)		52	(241)		135
Other comprehensive income (loss), net of tax		85		(104)	456		(270)
AOCI Attributable to Noncontrolling Interest
Accumulated Other Comprehensive Income [Roll Forward]
Other comprehensive income (loss), net of tax		(1)		2	(7)		4
AOCI Attributable to Parent
Accumulated Other Comprehensive Income [Roll Forward]
AOCI beginning balance		669		563	304		727
Other comprehensive income (loss), net of tax		84		(102)	449		(266)
AOCI ending balance		$ 753		$ 461	$ 753		$ 461

[1] The reclassification adjustment out of net unrealized gains on securities affected the following lines in AFG’s Statement of Earnings: OCI component Affected line in the statement of earnings Pretax Realized gains (losses) on securities Tax Provision for income taxes Attributable to noncontrolling interests Net earnings (loss) attributable to noncontrolling interests

[2] Includes net unrealized gains of $51 million at September 30, 2016 compared to $48 million at June 30, 2016 and $51 million at December 31, 2015 related to securities for which only the credit portion of an other-than-temporary impairment has been recorded in earnings.