Derivative Instruments (Cumulative Basis Adjustments For Fair Value Hedges) (Details) - Fixed Maturity Securities [Member] $ in Millions	Mar. 31, 2019 USD ($)
Derivatives, Fair Value [Line Items]
Amortized cost of hedged asset	$ 457
Cumulative amount of fair value hedging adjustmentst included in the amortized cost of hedged assets	$ 161

Amount of cumulative increase (decrease) in fair value of hedged asset in fair value hedge, attributable to hedged risk.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4EE
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL109999712-113959

Name:	us-gaap_HedgedAssetFairValueHedgeCumulativeIncreaseDecrease
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant