Investments (Securities Lending Programs) (Details) - Maturity Overnight [Member] $ in Millions	Dec. 31, 2020 USD ($)
Marketable Securities [Line Items]
Securities lending payable	$ 1,199
Cash [Member]
Marketable Securities [Line Items]
Securities lending payable	1,056
United States Government Securities [Member]
Marketable Securities [Line Items]
Securities lending payable	$ 143

The amount of cash received as security in return for loaning securities to another party.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-04(11))
-URI http://asc.fasb.org/extlink&oid=120401414&loc=d3e603758-122996

Name:	us-gaap_DepositsReceivedForSecuritiesLoanedAtCarryingValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant