v3.7.0.1
Debt (Debt) (Details) - USD ($)
$ in Millions
Mar. 31, 2017
Dec. 31, 2016
Debt Instrument [Line Items]    
Debt and Capital Lease Obligations $ 11,952 $ 12,179
Debt, Current 608 748
Long-term Debt, Excluding Current Maturities 11,344 11,431
Unsecured Debt [Member]    
Debt Instrument [Line Items]    
Debt and Capital Lease Obligations 3,413 3,412
Loans Payable [Member]    
Debt Instrument [Line Items]    
Debt and Capital Lease Obligations 3,405 3,165
Corporate Debt Securities [Member]    
Debt Instrument [Line Items]    
Debt and Capital Lease Obligations 1,841 2,290
Notes Payable, Other Payables [Member]    
Debt Instrument [Line Items]    
Debt and Capital Lease Obligations 1,561 1,597
Secured Debt [Member]    
Debt Instrument [Line Items]    
Debt and Capital Lease Obligations 1,550 1,553
Capital Lease Obligations [Member]    
Debt Instrument [Line Items]    
Debt and Capital Lease Obligations $ 157 $ 162