v3.8.0.1
Investments (Narrative) (Details) - USD ($)
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Investment [Line Items]      
Financing Receivable, Modifications, Pre-Modification Recorded Investment $ 0 $ 47,000,000  
Net change in unrealized gains (losses) from trading account assets 300,000,000 75,000,000 $ (642,000,000)
Fixed maturities, available-for-sale: [1] 346,780,000,000 321,419,000,000  
Other trading accounts [1] 5,752,000,000 5,764,000,000  
Other long-term investments [1] 12,308,000,000 11,283,000,000  
Fair value of securities 5,126,000,000 7,185,000,000  
Commercial mortgage and other loans, Acquired 0    
Commercial mortgage and other loans, Sold 2,000,000 0  
Troubled debt restructuring, Commitment to borrowers 0 0  
Troubled debt restructuring, Private debt commitments 5,000,000    
Consolidated feeder funds’ investments 451,000,000 216,000,000  
Unaffiliated interest 310,000,000 93,000,000  
Master funds gross assets 82,126,000,000 36,279,000,000  
Master funds gross liabilities 79,185,000,000 34,880,000,000  
Assets Deposited with Governmental Authorities 73,000,000 78,000,000  
Restricted Cash and Investments 45,000,000 54,000,000  
Assets Held in Voluntary Trusts 604,000,000 605,000,000  
Other Restricted Assets Held-in-trust 3,500,000,000 3,300,000,000  
Available-for-sale Securities, Restricted 59,000,000 89,000,000  
Carrying value of non-income producing assets [Member]      
Investment [Line Items]      
Fixed maturities, available-for-sale: 111,000,000    
Trading account assets supporting insurance liabilities 22,000,000    
Other trading accounts 1,000,000    
Other long-term investments 1,000,000    
Investments      
Investment [Line Items]      
Fair value of securities 599,000,000 1,595,000,000  
Cash      
Investment [Line Items]      
Fair value of securities 4,527,000,000 5,590,000,000  
Fixed maturities      
Investment [Line Items]      
Gross unrealized losses 1,776,000,000 4,625,000,000  
Gross unrealized losses of twelve months or more concentrated in various sectors 1,443,000,000 1,420,000,000  
Fixed maturities, available-for-sale: 346,780,000,000 321,419,000,000  
Fixed maturities | NAIC High or Highest Quality Rating      
Investment [Line Items]      
Gross unrealized losses 1,470,000,000 4,233,000,000  
Fixed maturities | NAIC Other Than High or Highest Quality Rating      
Investment [Line Items]      
Gross unrealized losses 306,000,000 392,000,000  
Corporate securities      
Investment [Line Items]      
Gross unrealized losses of twelve months or more concentrated in various sectors 1,443,000,000 1,420,000,000  
Equity securities      
Investment [Line Items]      
Gross unrealized losses 29,000,000 42,000,000  
Gross unrealized losses of twelve months or more concentrated in various sectors 1,000,000 1,000,000  
Other trading account assets | Subtotal other trading account assets excluding derivative      
Investment [Line Items]      
Net change in unrealized gains (losses) from trading account assets $ 256,000,000 164,000,000 $ (366,000,000)
California      
Investment [Line Items]      
Commercial mortgage loan, concentration percentage 27.00%    
Texas      
Investment [Line Items]      
Commercial mortgage loan, concentration percentage 9.00%    
NEW YORK      
Investment [Line Items]      
Commercial mortgage loan, concentration percentage 9.00%    
Europe      
Investment [Line Items]      
Commercial mortgage loan, concentration percentage 6.00%    
Asia      
Investment [Line Items]      
Commercial mortgage loan, concentration percentage 1.00%    
Declines in Value of 20% or More | Equity securities      
Investment [Line Items]      
Gross unrealized losses $ 8,000,000 9,000,000  
Declines in Value of 20% or More and in loss position for less than six months | Equity securities      
Investment [Line Items]      
Gross unrealized losses $ 5,000,000 $ 8,000,000  
[1] See Note 5 for details of balances associated with variable interest entities.