Condensed Financial Information of Parent Company - Condensed Statement of Cash Flows (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating Activities:
Net earnings (losses) attributable to shareholders	$ (29)	$ 204	$ 210	$ 145	$ 166	$ 11	$ 145	$ 153	$ 530	$ 475	$ 649
Adjustments:
Net cash provided by operating activities									2,083	1,804	1,150
Investing Activities:
Payments for (proceeds from) other investing activities									30	2	(83)
Net cash used in investing activities									(5,350)	(3,292)	(2,981)
Financing Activities:
Additional long-term borrowings									0	712	302
Reductions of long-term debt									0	(745)	(18)
Issuances of Common Stock									33	37	35
Repurchases of Common Stock									(6)	0	(133)
Cash dividends paid on Common Stock									(394)	(417)	(185)
Proceeds from (payments for) other financing activities									0	(4)	(13)
Net cash provided by (used in) financing activities									2,444	1,719	2,718
Net Change in Cash and Cash Equivalents									(823)	231	887
Cash and cash equivalents at beginning of year				2,338				2,107	2,338	2,107	1,220
Cash and cash equivalents at end of year	1,515				2,338				1,515	2,338	2,107
AFG
Operating Activities:
Net earnings (losses) attributable to shareholders									530	475	649
Adjustments:
Equity in net earnings of subsidiaries									(637)	(575)	(638)
Dividends from subsidiaries									238	580	611
Other operating activities, net									84	98	(67)
Net cash provided by operating activities									215	578	555
Investing Activities:
Capital contributions to subsidiaries									(11)	(93)	(560)
Returns of capital from subsidiaries									23	30	0
Purchases of investments, property and equipment									(5)	(2)	(1)
Proceeds from maturities and redemptions of investments									3	2	1
Net cash used in investing activities									10	(63)	(560)
Financing Activities:
Additional long-term borrowings									0	712	296
Reductions of long-term debt									0	(745)	0
Issuances of Common Stock									34	37	35
Repurchases of Common Stock									(6)	0	(133)
Cash dividends paid on Common Stock									(394)	(417)	(185)
Net cash provided by (used in) financing activities									(366)	(413)	13
Net Change in Cash and Cash Equivalents									(141)	102	8
Cash and cash equivalents at beginning of year				$ 299				$ 197	299	197	189
Cash and cash equivalents at end of year	$ 158				$ 299				$ 158	$ 299	$ 197