Basis of Presentation and Significant Accounting Policies Impact of Accounting Changes (Details) - USD ($) $ in Millions	Sep. 30, 2020	Jun. 30, 2020	Jan. 01, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Financing Receivable, before Allowance for Credit Loss				$ 4,215
Financing Receivable, Allowance for Credit Loss				0
Financing Receivable, after Allowance for Credit Loss				4,215
Premiums Receivable, Gross	$ 4,624			4,529
Premium Receivable, Allowance for Credit Loss	(174)	$ (183)		(145)
Premiums receivable and agents' balances, net of ACL	4,450			4,384
Reinsurance Recoverables, Gross	5,777			5,641
Reinsurance Recoverable, Allowance for Credit Loss	(55)	(54)		(48)
Reinsurance Recoverables, Including Reinsurance Premium Paid	5,668			5,527
Deferred income taxes, net	49			299
Other Liabilities	(4,585)			(5,157)
Retained earnings	13,503			12,685
Commercial Loan [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Financing Receivable, before Allowance for Credit Loss	4,499			4,215
Financing Receivable, Allowance for Credit Loss	(38)	(43)		0	$ 0	$ 0	$ (1)
Uncollectible reinsurance
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reinsurance Recoverable, Allowance for Credit Loss	$ (109)	(111)		(114)
Cumulative Effect, Period of Adoption, Adjustment [Member] | Accounting Standards Update 2016-13 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		0		(2)
Cumulative Effect, Period of Adoption, Adjustment [Member] | Commercial Loan [Member] | Accounting Standards Update 2016-13 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Retained earnings			$ (19)
Cumulative Effect, Period of Adoption, Adjustment [Member] | Retained Earnings | Accounting Standards Update 2016-13 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest			18
Cumulative Effect, Period of Adoption, Adjustment [Member] | Retained Earnings | Reinsurance Recoverable Including Reinsurance Premium Paid [Member] | Accounting Standards Update 2016-13 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest			(2)
Cumulative Effect, Period of Adoption, Adjustment [Member] | Retained Earnings | Deferred Income Tax Asset, Net [Member] | Accounting Standards Update 2016-13 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest			(5)
Cumulative Effect, Period of Adoption, Adjustment [Member] | Retained Earnings | Other liabilities | Accounting Standards Update 2016-13 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest			(25)
Cumulative Effect, Period of Adoption, Adjustment [Member] | Retained Earnings | Total Change to LCL and ACL [Member] | Accounting Standards Update 2016-13 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest			23
Cumulative Effect, Period of Adoption, Adjustment [Member] | Retained Earnings | Premiums Receivable [Member] | Accounting Standards Update 2016-13 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest			(23)
Cumulative Effect, Period of Adoption, Adjustment [Member] | Retained Earnings | Commercial Loan [Member] | Accounting Standards Update 2016-13 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest			(19)
Cumulative Effect, Period of Adoption, Adjusted Balance [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Financing Receivable, before Allowance for Credit Loss			4,215
Financing Receivable, Allowance for Credit Loss			(19)
Financing Receivable, after Allowance for Credit Loss			4,196
Premiums Receivable, Gross			4,529
Premium Receivable, Allowance for Credit Loss			(122)	(122)
Premiums receivable and agents' balances, net of ACL			4,407
Reinsurance Recoverables, Gross			5,641
Reinsurance Recoverable, Allowance for Credit Loss		(54)		$ (50)
Reinsurance Recoverables, Including Reinsurance Premium Paid			5,525
Deferred income taxes, net			304
Other Liabilities			(5,182)
Retained earnings			12,667
Cumulative Effect, Period of Adoption, Adjusted Balance [Member] | Commercial Loan [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Financing Receivable, Allowance for Credit Loss		$ 43	(19)
Cumulative Effect, Period of Adoption, Adjusted Balance [Member] | Uncollectible reinsurance
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reinsurance Recoverable, Allowance for Credit Loss			$ (116)