Commitments and Contingencies - Commitments and Contingencies (Details) - USD ($) $ in Millions	12 Months Ended		36 Months Ended
	Dec. 31, 2019	Dec. 31, 2016	Dec. 31, 2019	Dec. 31, 2018
Loss Contingencies [Line Items]
Other Commitment	$ 1,258		$ 1,258
Guaranty liabilities	89		89	$ 97
Fair value of derivative instrument in a net liability position	81		81
Collateral already posted	77		77
Additional collateral required	$ 5		5
Guarantor Obligations, Unlimited Exposure	The guarantees have no limitation as to maximum potential future payments.
Other Assets
Loss Contingencies [Line Items]
Premium tax offsets	$ 2		2	$ 2
Limited partnerships and other alternative investments
Loss Contingencies [Line Items]
Other Commitment	852		852
Private Placement Securities
Loss Contingencies [Line Items]
Other Commitment	191		191
Mortgage loans
Loss Contingencies [Line Items]
Other Commitment	215		215
Cancelable mortgage loan [Member]
Loss Contingencies [Line Items]
Other Commitment	130		130
Asbestos
Loss Contingencies [Line Items]
Liability for unpaid losses and loss adjustment expenses, at undiscounted amounts	874		874
Environmental
Loss Contingencies [Line Items]
Liability for unpaid losses and loss adjustment expenses, at undiscounted amounts	120		120
Asbestos and Environmental
Loss Contingencies [Line Items]
Liability for unpaid losses and loss adjustment expenses, at undiscounted amounts	1,147		1,147
Reinsurance Retention Policy, Excess Retention, Amount Reinsured	860
Reinsurance Retention Policy, Amount Retained		$ 1,700
Adverse development from comprehensive annual review	$ 640		$ 640
Insurance-related Assessments [Member]
Loss Contingencies [Line Items]
Minimum Percentage of Premiums Written Per Year to be Considered for Assessment Under Guaranty Fund	1.00%
Maximum Percentage of Premiums Written Per Year to be Considered for Assessment Under Guaranty Fund	2.00%