Accumulated Other Comprehensive Income Loss Level 4- Reclassifications from AOCI (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net realized capital gains (losses)	$ (30)	$ 25
Income before income taxes	519	401
Net investment income	451	410
Income tax expense	91	98
Income (Loss) from Discontinued Operations, Net of Tax	169	75
Net Income (Loss) Attributable to Parent	597	378
Operating Expenses	1,037	919
Amount Reclassified from AOCI
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net Income (Loss) Attributable to Parent	(23)	27
Net Unrealized Gain on Securities | Amount Reclassified from AOCI
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net realized capital gains (losses)	(38)	14
Income before income taxes	(38)	14
Income tax expense	(8)	5
Income (Loss) from Discontinued Operations, Net of Tax	3	14
Net Income (Loss) Attributable to Parent	(27)	23
Net Gain on Cash Flow Hedging Instruments | Amount Reclassified from AOCI
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income before income taxes	9	13
Income tax expense	2	4
Income (Loss) from Discontinued Operations, Net of Tax	6	5
Net Income (Loss) Attributable to Parent	13	14
Amortization of Prior Service Credit | Amount Reclassified from AOCI
Accumulated Other Comprehensive Income (Loss) [Line Items]
Operating Expenses	1	1
Amortization of Actuarial Loss | Amount Reclassified from AOCI
Accumulated Other Comprehensive Income (Loss) [Line Items]
Operating Expenses	(13)	(16)
Pension and Other Postretirement Plan Adjustments | Amount Reclassified from AOCI
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income before income taxes	(12)	(15)
Income tax expense	(3)	(5)
Net Income (Loss) Attributable to Parent	(9)	(10)
Interest Rate Swap [Member] | Net Gain on Cash Flow Hedging Instruments | Amount Reclassified from AOCI
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net realized capital gains (losses)	1	4
Net investment income	$ 8	$ 9