Business, Basis of Presentation and Significant Accounting Policies - Adoption of New Pronouncements (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019	Dec. 31, 2018	Jan. 01, 2020	Jun. 30, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member	us-gaap:AccountingStandardsUpdate201613Member	us-gaap:AccountingStandardsUpdate201802Member
Unappropriated	$ (4,833)	$ (4,649)
Premium receivable and reinsurance recoverable, allowance for credit losses	24	0
Deferred policy acquisition costs and Value of business acquired	$ 1,967	2,226	$ 2,973		$ 2,418
Accounting Standards Update 2016-13
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs and Value of business acquired		$ 3
Accounting Standards Update 2016-13 | Retained Earnings (Deficit), Unappropriated
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Unappropriated				$ (33)
Mortgage loans on real estate | Accounting Standards Update 2016-13
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accounts Receivable, Allowance for Credit Loss				19
Reinsurance Recoverables | Accounting Standards Update 2016-13
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Premium receivable and reinsurance recoverable, allowance for credit losses				28
deferred policy acquisition cost | Accounting Standards Update 2016-13
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs and Value of business acquired				5
Deferred Income Tax Charge | Accounting Standards Update 2016-13
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred Tax Assets, Deferred Income				$ 9