Segment information Segment Information (narrative Detail (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Segment Reporting Information [Line Items]
Derivative, (Gain) Loss on Derivative, Net	$ (63)	$ 206	$ (90)	$ 490
Net investment income	770	708	1,515	1,382
North America Agricultural Insurance [Member]
Segment Reporting Information [Line Items]
Segment Income Loss Including Gains Losses On Crop Derivatives			23
Derivative, (Gain) Loss on Derivative, Net			2
Net investment income	6	5	12	10
Segment Life [Member]
Segment Reporting Information [Line Items]
Net investment income	77	$ 69	$ 152	$ 136
Management Underwriting Income (Loss)	56
Gains Losses On Fair Value Changes In Separate Account Assets	$ 16