v3.8.0.1
Debt (Debt) (Details) - USD ($)
$ in Millions
Sep. 30, 2017
Dec. 31, 2016
Debt Instrument [Line Items]    
Debt and Capital Lease Obligations $ 11,650 $ 12,179
Debt, Current 369 748
Long-term Debt, Excluding Current Maturities 11,281 11,431
Unsecured Debt [Member]    
Debt Instrument [Line Items]    
Debt and Capital Lease Obligations 3,415 3,412
Loans Payable [Member]    
Debt Instrument [Line Items]    
Debt and Capital Lease Obligations 3,152 3,165
Corporate Debt Securities [Member]    
Debt Instrument [Line Items]    
Debt and Capital Lease Obligations 1,843 2,290
Notes Payable, Other Payables [Member]    
Debt Instrument [Line Items]    
Debt and Capital Lease Obligations 1,575 1,597
Secured Debt [Member]    
Debt Instrument [Line Items]    
Debt and Capital Lease Obligations 1,544 1,553
Capital Lease Obligations [Member]    
Debt Instrument [Line Items]    
Debt and Capital Lease Obligations $ 121 $ 162