Closed Block (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Policyholders’ dividend obligation	$ 5,446	$ 4,658	$ 4,509
Dividend Declared
Increase (decrease) in liability	(86)	32	$ 58
Excess Of Actual Cumulative Earnings Over Expected Cumulative Earnings
Policyholders’ dividend obligation	1,790	1,647
Net Unrealized Gains (Losses) on Investments
Policyholders’ dividend obligation	$ 3,656	$ 3,011

The liability as of the balance sheet date for the excess of the cumulative actual closed block earnings over the cumulative expected (actuarially determined) closed block earnings (each) for the period from the actuarial calculation date to the date of measurement. The excess will result in future dividends to closed block policyholders, unless offset by less favorable than expected future performance of the closed block. The policyholder dividend obligation, which may not have a negative balance, recognizes that a portion of earnings in certain cases will not inure to the stockholders of the insurance entity.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 805
-Section 55
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=84167291&loc=d3e31071-158570

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 805
-Section 50
-Paragraph 3
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=6487222&loc=d3e30806-158569

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