Consolidated Statement of Changes in Equity (Unaudited) - USD ($) $ in Millions		Total	Total	Common Shares	Common Stock and Capital Surplus	Retained Earnings	Accumulated Other Comp. Income (Loss)	Noncontrolling interests
Beginning Balance, shares at Dec. 31, 2016				86,924,399
Beginning Balance at Dec. 31, 2016		$ 4,919	$ 4,916		$ 1,198	$ 3,343	$ 375	$ 3
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings (losses) attributable to parent		298	298			298
Net earnings (losses) including portion attributable to nonredeemable noncontrolling interest		300						2
Other comprehensive income (loss)		240	240				240	0
Dividends on Common Stock		(187)	(187)			(187)
Shares issued:
Exercise of stock options, shares				792,288
Exercise of stock options		26	26		26
Restricted stock awards, shares				232,250
Restricted stock awards		0	0		0
Other benefit plans, shares				75,381
Other benefit plans		7	7		7
Dividend reinvestment plan, shares				19,516
Dividend reinvestment plan		2	2		2
Stock-based compensation expense		13	13		13
Shares exchanged — benefit plans, shares				(32,509)
Shares exchanged — benefit plans		(3)	(3)		0	(3)
Forfeitures of restricted stock, shares				(4,073)
Forfeitures of restricted stock		0	0		0
Other		(5)						(5)
Ending Balance, shares at Jun. 30, 2017				88,007,252
Ending Balance at Jun. 30, 2017		5,312	5,312		1,246	3,451	615	0
Beginning Balance, Redeemable Noncontrolling Interests at Dec. 31, 2016		0
Ending Balance, Redeemable Noncontrolling Interests at Jun. 30, 2017		0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of accounting change	[1]						0
Cumulative effect of accounting change		$ 4	4			225	(221)
Beginning Balance, shares at Dec. 31, 2017		88,275,460		88,275,460
Beginning Balance at Dec. 31, 2017		$ 5,331	5,330		1,269	3,248	813	1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings (losses) attributable to parent		355	355			355
Net earnings (losses) including portion attributable to nonredeemable noncontrolling interest		354						(1)
Other comprehensive income (loss)		(445)	(445)				(445)	0
Dividends on Common Stock		(196)	(196)			(196)
Shares issued:
Exercise of stock options, shares				531,726
Exercise of stock options		19	19		19
Restricted stock awards, shares				200,625
Restricted stock awards		0	0		0
Other benefit plans, shares				73,676
Other benefit plans		8	8		8
Dividend reinvestment plan, shares				18,006
Dividend reinvestment plan		2	2		2
Stock-based compensation expense		11	11		11
Shares exchanged — benefit plans, shares				(24,310)
Shares exchanged — benefit plans		(2)	(2)		0	(2)
Forfeitures of restricted stock, shares				(3,069)
Forfeitures of restricted stock		0	0		0
Other		$ (2)	(2)			(2)		0
Ending Balance, shares at Jun. 30, 2018		89,072,114		89,072,114
Ending Balance at Jun. 30, 2018		$ 5,084	$ 5,084		$ 1,309	$ 3,628	147	$ 0
Beginning Balance, Redeemable Noncontrolling Interests at Dec. 31, 2017		3
Redeemable Noncontrolling Interest, Equity, Carrying Amount [Abstract]
Net earnings attributable to redeemable noncontrolling interests		(5)
Other		2
Ending Balance, Redeemable Noncontrolling Interests at Jun. 30, 2018		$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of accounting change	[1]						$ 0

[1] On January 1, 2018, AFG adopted new guidance that requires all equity securities other than those accounted for under the equity method to be reported at fair value with holding gains and losses recognized in net earnings. At the date of adoption, the $221 million net unrealized gain on equity securities classified as available for sale (with unrealized holding gains and losses reported in AOCI) under the prior guidance was reclassified from AOCI to retained earnings as the cumulative effect of an accounting change.