Derivative Financial Instruments (Narrative) (Details) - USD ($)
$ in Millions |
Jun. 30, 2016 |
Dec. 31, 2015 |
Dec. 31, 2014 |
Dec. 31, 2013 |
Dec. 31, 2012 |
| Derivative Instruments, Gain (Loss) [Line Items] |
|
|
|
|
|
| Accumulated other comprehensive income (loss) |
$ (19)
|
$ 2
|
$ 8
|
$ (5)
|
$ (2)
|
| Interest rate cash flow hedge gain (loss) to be reclassified during next 12 months |
(8)
|
(7)
|
|
|
|
| Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral |
19
|
14
|
|
|
|
| Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral |
116
|
41
|
|
|
|
| Central Counterparty Clearing House |
|
|
|
|
|
| Derivative Instruments, Gain (Loss) [Line Items] |
|
|
|
|
|
| Collateral Already Posted, Aggregate Fair Value |
32
|
7
|
|
|
|
| Not Designated as Hedging Instrument |
|
|
|
|
|
| Derivative Instruments, Gain (Loss) [Line Items] |
|
|
|
|
|
| Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral |
19
|
14
|
36
|
|
|
| Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral |
81
|
22
|
|
|
|
| Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent |
|
|
|
|
|
| Derivative Instruments, Gain (Loss) [Line Items] |
|
|
|
|
|
| Accumulated other comprehensive income (loss) |
$ (40)
|
$ (3)
|
$ 0
|
$ 0
|
$ 0
|