v3.8.0.1
Investments (Analysis of Past Due Commercial Mortgage and Other Loans) (Details) - USD ($)
$ in Millions
Dec. 31, 2017
Dec. 31, 2016
Financing Receivable, Recorded Investment, Past Due [Line Items]    
Current $ 56,144 $ 52,851
Total Past Due 7 34
Total Loans 56,151 52,885
Non-Accrual Status(2) 96 54
30-59 Days Past Due    
Financing Receivable, Recorded Investment, Past Due [Line Items]    
Total Past Due 3 28
60-89 Days Past Due    
Financing Receivable, Recorded Investment, Past Due [Line Items]    
Total Past Due 0 1
Greater Than 90 Days    
Financing Receivable, Recorded Investment, Past Due [Line Items]    
Total Past Due 4 5
Commercial Mortgage Loans    
Financing Receivable, Recorded Investment, Past Due [Line Items]    
Current 52,084 49,006
Total Past Due 0 21
Total Loans 52,084 49,027
Non-Accrual Status(2) 71 49
Commercial Mortgage Loans | 30-59 Days Past Due    
Financing Receivable, Recorded Investment, Past Due [Line Items]    
Total Past Due 0 21
Commercial Mortgage Loans | 60-89 Days Past Due    
Financing Receivable, Recorded Investment, Past Due [Line Items]    
Total Past Due 0 0
Commercial Mortgage Loans | Greater Than 90 Days    
Financing Receivable, Recorded Investment, Past Due [Line Items]    
Total Past Due 0 0
Agricultural property loans    
Financing Receivable, Recorded Investment, Past Due [Line Items]    
Current 3,201 2,956
Total Past Due 2 2
Total Loans 3,203 2,958
Non-Accrual Status(2) 23 2
Agricultural property loans | 30-59 Days Past Due    
Financing Receivable, Recorded Investment, Past Due [Line Items]    
Total Past Due 0 0
Agricultural property loans | 60-89 Days Past Due    
Financing Receivable, Recorded Investment, Past Due [Line Items]    
Total Past Due 0 0
Agricultural property loans | Greater Than 90 Days    
Financing Receivable, Recorded Investment, Past Due [Line Items]    
Total Past Due 2 2
Residential property loans    
Financing Receivable, Recorded Investment, Past Due [Line Items]    
Current 191 241
Total Past Due 5 11
Total Loans 196 252
Non-Accrual Status(2) 2 3
Residential property loans | 30-59 Days Past Due    
Financing Receivable, Recorded Investment, Past Due [Line Items]    
Total Past Due 3 7
Residential property loans | 60-89 Days Past Due    
Financing Receivable, Recorded Investment, Past Due [Line Items]    
Total Past Due 0 1
Residential property loans | Greater Than 90 Days    
Financing Receivable, Recorded Investment, Past Due [Line Items]    
Total Past Due 2 3
Other collateralized loans    
Financing Receivable, Recorded Investment, Past Due [Line Items]    
Current 5 10
Total Past Due 0 0
Total Loans 5 10
Non-Accrual Status(2) 0 0
Other collateralized loans | 30-59 Days Past Due    
Financing Receivable, Recorded Investment, Past Due [Line Items]    
Total Past Due 0 0
Other collateralized loans | 60-89 Days Past Due    
Financing Receivable, Recorded Investment, Past Due [Line Items]    
Total Past Due 0 0
Other collateralized loans | Greater Than 90 Days    
Financing Receivable, Recorded Investment, Past Due [Line Items]    
Total Past Due 0 0
Uncollateralized loans    
Financing Receivable, Recorded Investment, Past Due [Line Items]    
Current 663 638
Total Past Due 0 0
Total Loans 663 638
Non-Accrual Status(2) 0 0
Uncollateralized loans | 30-59 Days Past Due    
Financing Receivable, Recorded Investment, Past Due [Line Items]    
Total Past Due 0 0
Uncollateralized loans | 60-89 Days Past Due    
Financing Receivable, Recorded Investment, Past Due [Line Items]    
Total Past Due 0 0
Uncollateralized loans | Greater Than 90 Days    
Financing Receivable, Recorded Investment, Past Due [Line Items]    
Total Past Due $ 0 $ 0