Notes Payable - Earliest Interest Reset Date of Borrowing Outstanding (Details) - USD ($)
$ in Thousands |
12 Months Ended |
Dec. 31, 2015 |
Dec. 31, 2014 |
| Schedule of Short-term and Long-term Borrowings [Line Items] |
|
|
| Meduim Term Notes Called During the Period |
$ 2,400,000
|
$ 500,000
|
| Due within one year |
$ 9,111,461
|
$ 7,353,953
|
| Short-term Debt, Weighted Average Interest Rate |
0.48%
|
0.32%
|
| Long-term Debt, Maturities, Repayments of Principal in Year Two |
$ 1,200,558
|
$ 1,569,961
|
| Long-term Debt, Maturities, Repayments of Principal in Year Three |
1,539,264
|
1,219,192
|
| Long-term Debt, Maturities, Repayments of Principal in Year Four |
520,284
|
682,224
|
| Long-term Debt, Maturities, Repayments of Principal in Year Five |
529,567
|
872,576
|
| Long-term Debt, Maturities, Repayments of Principal after Year Five |
1,177,363
|
1,127,233
|
| Debt and Capital Lease Obligations |
$ 14,078,497
|
$ 12,825,139
|
| Long-term Debt, Weighted Average Interest Rate |
1.59%
|
1.56%
|
| Debt, Weighted Average Interest Rate |
0.87%
|
0.85%
|
| Due within one year [Member] |
|
|
| Schedule of Short-term and Long-term Borrowings [Line Items] |
|
|
| Due within one year |
$ 10,560,504
|
|
| Short-term Debt, Weighted Average Interest Rate |
0.55%
|
|
| Due year two [Member] |
|
|
| Schedule of Short-term and Long-term Borrowings [Line Items] |
|
|
| Long-term Debt, Maturities, Repayments of Principal in Year Two |
$ 1,071,581
|
|
| Long-term Debt, Weighted Average Interest Rate |
1.06%
|
|
| Due year three [Member] |
|
|
| Schedule of Short-term and Long-term Borrowings [Line Items] |
|
|
| Long-term Debt, Maturities, Repayments of Principal in Year Three |
$ 737,333
|
|
| Long-term Debt, Weighted Average Interest Rate |
1.32%
|
|
| Due year four [Member] |
|
|
| Schedule of Short-term and Long-term Borrowings [Line Items] |
|
|
| Long-term Debt, Maturities, Repayments of Principal in Year Four |
$ 520,284
|
|
| Long-term Debt, Weighted Average Interest Rate |
1.73%
|
|
| Due year five [Member] |
|
|
| Schedule of Short-term and Long-term Borrowings [Line Items] |
|
|
| Long-term Debt, Maturities, Repayments of Principal in Year Five |
$ 298,764
|
|
| Long-term Debt, Weighted Average Interest Rate |
1.76%
|
|
| Due after five years [Member] |
|
|
| Schedule of Short-term and Long-term Borrowings [Line Items] |
|
|
| Long-term Debt, Maturities, Repayments of Principal after Year Five |
$ 890,031
|
|
| Long-term Debt, Weighted Average Interest Rate |
3.34%
|
|