Shareholders' Equity - Progression of the components of accumulated other comprehensive income (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Accumulated Other Comprehensive Income [Roll Forward]
AOCI beginning balance		$ 304
Other comprehensive income (loss), net of tax		67		$ (431)		$ 170
Other comprehensive income (loss), net of tax, acquisition of noncontrolling interest		(315)
AOCI ending balance		375		304
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		124		(625)		334
Other comprehensive income (loss), unrealized holding gains on securities arising during the period, tax		(44)		219		(118)
Other comprehensive income (loss), unrealized holding gains on securities arising during the period, net of tax		80		(406)		216
Reclassification from accumulated other comprehensive income, pretax	[1]	(19)		14		(52)
Reclassification from accumulated other comprehensive income, tax	[1]	7		(5)		19
Reclassification from accumulated other comprehensive income, net of tax		(12)		9		(33)
Accumulated Other Comprehensive Income [Roll Forward]
Other comprehensive income (loss), pretax		105		(645)		282
Other comprehensive income (loss), tax		(37)		226		(99)
Other comprehensive income (loss), net of tax		68		(419)		183
Accumulated net investment gain (loss) including portion attributable to noncontrolling interest | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from accumulated other comprehensive income, pretax				(34)
Reclassification from accumulated other comprehensive income, tax				12
Reclassification from accumulated other comprehensive income, net of tax				(22)
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		(4)		9		(4)
Reclassification from accumulated other comprehensive income, net of tax	[1]	(1)		(1)		1
Accumulated Other Comprehensive Income [Roll Forward]
Other comprehensive income (loss), net of tax		(5)		8		(3)
Accumulated net investment gain (loss) attributable to noncontrolling interest | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from accumulated other comprehensive income, net of tax				0
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		76		(397)		212
Reclassification from accumulated other comprehensive income, net of tax		(13)		8		(32)
Accumulated Other Comprehensive Income [Roll Forward]
AOCI beginning balance		332	[2]	743	[2]	563
Other comprehensive income (loss), net of tax		63		(411)		180
Other comprehensive income (loss), net of tax, acquisition of noncontrolling interest		9
AOCI ending balance	[2]	404		332		743
Accumulated net investment gain (loss) attributable to parent | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from accumulated other comprehensive income, net of tax				(22)
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		(12)		1
Other comprehensive income (loss), tax		4		0
Other comprehensive income (loss), net of tax		(8)		1
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
Accumulated net gain (loss) from cash flow hedges attributable to parent
Accumulated Other Comprehensive Income [Roll Forward]
AOCI beginning balance		1		0
Other comprehensive income (loss), net of tax		(8)		1
AOCI ending balance		(7)		1		0
Accumulated foreign currency adjustment including portion attributable to noncontrolling interest
Accumulated Other Comprehensive Income [Roll Forward]
Other comprehensive income (loss), pretax		6		(9)		(8)
Other comprehensive income (loss), tax		1		(5)		(1)
Other comprehensive income (loss), net of tax		7		(14)		(9)
Accumulated foreign currency adjustment attributable to noncontrolling interest
Accumulated Other Comprehensive Income [Roll Forward]
Other comprehensive income (loss), net of tax		0		0		0
Accumulated foreign currency adjustment attributable to parent
Accumulated Other Comprehensive Income [Roll Forward]
AOCI beginning balance		(22)		(8)		1
Other comprehensive income (loss), net of tax		7		(14)		(9)
AOCI ending balance		(15)		(22)		(8)
Accumulated defined benefit plans adjustment including portion attributable to noncontrolling interest
Accumulated Other Comprehensive Income [Roll Forward]
Other comprehensive income (loss), pretax		0		1		(6)
Other comprehensive income (loss), tax		0		0		2
Other comprehensive income (loss), net of tax		0		1		(4)
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
Accumulated defined benefit plans adjustment attributable to parent
Accumulated Other Comprehensive Income [Roll Forward]
AOCI beginning balance		(7)		(8)		(4)
Other comprehensive income (loss), net of tax		0		1		(4)
AOCI ending balance		(7)		(7)		(8)
AOCI including portion attributable to noncontrolling interest
Accumulated Other Comprehensive Income [Roll Forward]
Other comprehensive income (loss), pretax		99		(652)		268
Other comprehensive income (loss), tax		(32)		221		(98)
Other comprehensive income (loss), net of tax		67		(431)		170
AOCI attributable to noncontrolling interest
Accumulated Other Comprehensive Income [Roll Forward]
Other comprehensive income (loss), net of tax		(5)		8		(3)
AOCI attributable to parent
Accumulated Other Comprehensive Income [Roll Forward]
AOCI beginning balance		304		727		560
Other comprehensive income (loss), net of tax		62		(423)		167
Other comprehensive income (loss), net of tax, acquisition of noncontrolling interest		9
AOCI ending balance		$ 375		$ 304		$ 727

[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 $52 million at December 31, 2016 compared to net unrealized gains of $51 million and $58 million at December 31, 2015 and 2014, related to securities for which only the credit portion of an other-than-temporary impairment has been recorded in earnings.