Business Dispositions and Discontinued Operations - Additional Information (Details) - USD ($)			12 Months Ended
	Dec. 03, 2017	May 10, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loss on discontinued operations			$ 3,257,000,000	$ 81,000,000	$ (6,000,000)
Reinsurance recoverables, net			4,061,000,000	3,659,000,000
Operating Segments | Property and Casualty Insurance Products
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Reinsurance recoverables, net			3,476,000,000	3,085,000,000
Operating Segments | Commercial Lines | Property and Casualty Insurance Products
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Liability for unpaid losses and loss adjustment expense, held for sale			688,000,000	712,000,000	743,000,000
Reinsurance recoverables, net			688,000,000	712,000,000
Disposal Group, Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Capital loss from transaction		$ 5,000,000
Disposal Group, Disposed of by Sale, Not Discontinued Operations | P&C Runoff Subsidiaries
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash proceeds from sale of business		$ 272,000,000
Discontinued Operations, Held-for-sale | Run-Off Life and Annuity Business
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash proceeds from sale of business	$ 1.4
Loss on discontinued operations			3,257,000,000	0	$ 0
Dividends paid	$ 0
Ownership interest retained, percentage	9.70%
Ownership interest retained	$ 164,000,000
Reduction in long term debt	142,000,000		142,000,000	142,000,000
Consideration received	$ 1,500,000,000
Income tax benefits retained			700,000,000
Operating loss carryforwards retained			437,000,000
Tax credits retained			235,000,000
Adjustments to AOCI			1,000,000,000
Management agreement term	5 years
Discontinued Operations, Held-for-sale | Run-Off Life and Annuity Business | Minimum
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Transition services agreement term	12 months
Discontinued Operations, Held-for-sale | Run-Off Life and Annuity Business | Maximum
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Transition services agreement term	24 months
Discontinued Operations, Held-for-sale | Run-Off Life and Annuity Business | Operating Segments | Commercial Lines | Property and Casualty Insurance Products
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Liability for unpaid losses and loss adjustment expense, held for sale			688,000,000	712,000,000
Reinsurance recoverables, net			$ 688,000,000	$ 712,000,000