Accumulated Other Comprehensive Income Loss - Reclassifications from AOCI (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net realized capital gains	$ 52	$ 57	$ 22	$ 82
Income from continuing operations before income taxes	537	(281)	1,056	120
Net investment income	428	395	879	805
Income tax expense (benefit)	103	(129)	194	(31)
Income from discontinued operations, net of tax	148	112	317	187
Net income (loss)	582	(40)	1,179	338
Insurance operating costs and other expenses	1,067	1,650	2,104	2,569
Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net income (loss)	(13)	(419)	(37)	(392)
Net Unrealized Gain on Securities | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net realized capital gains	(6)	56	(44)	71
Income from continuing operations before income taxes	(6)	56	(44)	71
Income tax expense (benefit)	(1)	20	(9)	25
Income from discontinued operations, net of tax	(5)	26	(2)	39
Net income (loss)	(10)	62	(37)	85
Accumulated Other-than-Temporary Impairment Attributable to Parent [Member] | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net realized capital gains	0		0
Income from continuing operations before income taxes	0		0
Income tax expense (benefit)	0		0
Income from discontinued operations, net of tax	1		1
Net income (loss)	1		1
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income from continuing operations before income taxes	9	11	18	24
Income tax expense (benefit)	2	4	4	8
Income from discontinued operations, net of tax	(1)	7	5	11
Net income (loss)	6	14	19	27
Amortization of prior service credit | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Insurance operating costs and other expenses	2	2	3	3
Amortization of actuarial loss | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Insurance operating costs and other expenses	(15)	(16)	(28)	(32)
Settlement loss | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Settlement loss		(747)		(747)
Pension and Other Postretirement Plan Adjustments | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income from continuing operations before income taxes	(13)	(761)	(25)	(776)
Income tax expense (benefit)	(3)	(266)	(5)	(272)
Net income (loss)	(10)	(495)	(20)	(504)
Interest rate swaps | Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net realized capital gains	0	1	1	5
Net investment income	$ 9	$ 10	$ 17	$ 19