Claim and Claim Adjustment Expense Reserves (Life & Group Policyholder Reserves) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2019
Liability for Claims and Claims Adjustment Expense [Abstract]
Liability for unpaid claims and claims adjustment expense, period increase (decrease)	$ 56	$ 31
Premium deficiency and future policy benefit	$ 216		$ 216

Amount, after effects of reinsurance, of increase (decrease) in the liability for unpaid claims and claims adjustment expense.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 40
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=116884095&loc=d3e14764-158437

Name:	us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpensePeriodIncreaseDecrease
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration