Variable Annuity and Insurance Guarantees (Separate Account Balances by Type) (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Mutual funds
Variable Annuity and Insurance Guarantees
Total mutual funds	$ 72,702	$ 74,676
Equity [Member]
Variable Annuity and Insurance Guarantees
Total mutual funds	43,724	46,038
Bond [Member]
Variable Annuity and Insurance Guarantees
Total mutual funds	22,577	23,529
Other [Member]
Variable Annuity and Insurance Guarantees
Total mutual funds	$ 6,401	$ 5,109

Fair value amount of the specified investment category of assets maintained in separate accounts as of the balance sheet date.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 20
-Section 55
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=6588021&loc=d3e7104-158389

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 80
-Section 50
-Paragraph 1
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=6484115&loc=d3e19393-158473

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