Investments - Commerical Mortgage Loans by Property Type and Geographic Region (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Mortgage Loans on Real Estate [Line Items]
Commercial Mortgage Loans	$ 1,666	$ 1,864
Pacific Region [Member]
Mortgage Loans on Real Estate [Line Items]
Commercial Mortgage Loans	714	738
South Atlantic Region [Member]
Mortgage Loans on Real Estate [Line Items]
Commercial Mortgage Loans	268	366
New England Region [Member]
Mortgage Loans on Real Estate [Line Items]
Commercial Mortgage Loans	227	276
Central Region [Member]
Mortgage Loans on Real Estate [Line Items]
Commercial Mortgage Loans	239	205
Middle Atlantic [Member]
Mortgage Loans on Real Estate [Line Items]
Commercial Mortgage Loans	186	227
Mountain [Member]
Mortgage Loans on Real Estate [Line Items]
Commercial Mortgage Loans	32	52
Office Buildings [Member]
Mortgage Loans on Real Estate [Line Items]
Commercial Mortgage Loans	592	697
Apartment Buildings [Member]
Mortgage Loans on Real Estate [Line Items]
Commercial Mortgage Loans	428	366
Industrial [Member]
Mortgage Loans on Real Estate [Line Items]
Commercial Mortgage Loans	302	322
Hotels [Member]
Mortgage Loans on Real Estate [Line Items]
Commercial Mortgage Loans	205	259
Retail Facilities [Member]
Mortgage Loans on Real Estate [Line Items]
Commercial Mortgage Loans	139	213
Other Property [Member]
Mortgage Loans on Real Estate [Line Items]
Commercial Mortgage Loans	$ 0	$ 7