Variable Interest Entities (Consolidated Variable Interest Entity Asset and Liability Information) (Details) $ in Millions		Dec. 31, 2017 USD ($) item	Dec. 31, 2016 USD ($) item
Disclosure Of Variable Interest Entities Assets And Liabilities [Line Items]
Number of Instruments | item		1	2
Notional Amounts		$ 573	$ 733
Carrying Value			$ 200
Total Return Swap [Member]
Disclosure Of Variable Interest Entities Assets And Liabilities [Line Items]
Number of Instruments | item		1	1
Notional Amounts		$ 573	$ 533
Credit Default Swaps [Member]
Disclosure Of Variable Interest Entities Assets And Liabilities [Line Items]
Number of Instruments | item			1
Notional Amounts			$ 200
Fixed maturity securities [Member] | Asset-backed credit card loans [Member]
Disclosure Of Variable Interest Entities Assets And Liabilities [Line Items]
Number of Instruments | item	[1]
Notional Amounts	[1]
Carrying Value	[1]		$ 200

[1] Reported in variable interest entities' fixed maturity securities on our Consolidated Balance Sheets.