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		309	309			309
Net earnings (losses) including portion attributable to nonredeemable noncontrolling interest		311						2
Other comprehensive income (loss)		314	314				314
Dividends on Common Stock		(214)	(214)			(214)
Shares issued:
Exercise of stock options, shares				870,022
Exercise of stock options		29	29		29
Restricted stock awards, shares				232,250
Other benefit plans, shares				85,190
Other benefit plans		8	8		8
Dividend reinvestment plan, shares				22,243
Dividend reinvestment plan		2	2		2
Stock-based compensation expense		18	18		18
Shares exchanged — benefit plans, shares				(34,922)
Shares exchanged — benefit plans		(3)	(3)			(3)
Forfeitures of restricted stock, shares				(6,388)
Other		(5)						(5)
Ending Balance, shares at Sep. 30, 2017				88,092,794
Ending Balance at Sep. 30, 2017		5,379	5,379		1,255	3,435	689	0
Ending Balance, Redeemable Noncontrolling Interests at Sep. 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		559	559			559
Net earnings (losses) including portion attributable to nonredeemable noncontrolling interest		558						(1)
Other comprehensive income (loss)		(548)	(548)				(548)
Dividends on Common Stock		(227)	(227)			(227)
Shares issued:
Exercise of stock options, shares				635,364
Exercise of stock options		23	23		23
Restricted stock awards, shares				200,625
Other benefit plans, shares				86,229
Other benefit plans		10	10		10
Dividend reinvestment plan, shares				21,072
Dividend reinvestment plan		2	2		2
Stock-based compensation expense		17	17		17
Shares exchanged — benefit plans, shares				(26,520)
Shares exchanged — benefit plans		(3)	(3)		(1)	(2)
Forfeitures of restricted stock, shares				(3,522)
Other		$ (3)	(3)			(3)
Ending Balance, shares at Sep. 30, 2018		89,188,708		89,188,708
Ending Balance at Sep. 30, 2018		$ 5,164	$ 5,164		$ 1,320	$ 3,800	44	$ 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		(6)
Other		3
Ending Balance, Redeemable Noncontrolling Interests at Sep. 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.