Segment information Segment Information (narrative Detail (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Gain (Loss) on Derivative	$ (17)	$ (22)	$ 91	$ 68
Net investment income	823	813	2,457	2,328
North America Agricultural Insurance [Member]
Segment Reporting Information [Line Items]
Segment Income Loss Including Gains Losses On Crop Derivatives	79
Gain (Loss) on Derivative	(8)
Net investment income	7	6	20	18
Segment Life [Member]
Segment Reporting Information [Line Items]
Net investment income	85	$ 78	$ 253	$ 230
Management Underwriting Income (Loss)	84
Gains(Losses) On Fair Value Changes In Separate Account Assets	$ (14)