Accumulated Other Comprehensive Income Loss - Reclassifications from AOCI (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net realized capital gains	$ 39	$ 27	$ 61	$ 109
Income from continuing operations before income taxes	530	181	1,586	301
Net investment income	444	404	1,323	1,209
Income tax expense	103	36	297	5
Income from discontinued operations, net of tax	5	89	322	276
Net income	432	234	1,611	572
Insurance operating costs and other expenses	1,091	952	3,195	3,521
Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net income	(15)	40	(52)	(356)
Net Unrealized Gain on Securities | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net realized capital gains	(15)	32	(59)	102
Income from continuing operations before income taxes	(15)	32	(59)	102
Income tax expense	(3)	11	(12)	36
Income from discontinued operations, net of tax	0	13	(2)	53
Net income	(12)	34	(49)	119
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	0		0
Income from discontinued operations, net of tax	0		1
Net income	0		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	7	8	25	32
Income tax expense	1	3	5	11
Income from discontinued operations, net of tax	0	7	5	19
Net income	6	12	25	40
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	5	0
Amortization of actuarial loss | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Insurance operating costs and other expenses	(14)	(12)	(42)	(45)
Settlement loss | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Settlement loss		0		(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	(12)	(10)	(37)	(792)
Income tax expense	(3)	(4)	(8)	(277)
Net income	(9)	(6)	(29)	(515)
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	0	1	5
Net investment income	$ 7	$ 8	$ 24	$ 27