Investment Securities (Details) - USD ($)
$ in Millions |
Jun. 30, 2016 |
Dec. 31, 2015 |
Dec. 31, 2014 |
| Available-for-sale securities |
|
|
|
| Amortized Cost |
$ 1,118
|
$ 1,294
|
$ 1,661
|
| Gross Unrealized Gains |
27
|
5
|
14
|
| Gross Unrealized Losses |
0
|
(5)
|
(3)
|
| Fair Value |
1,145
|
1,294
|
1,672
|
| Held-to-maturity securities |
|
|
|
| Amortized Cost |
1,211
|
1,268
|
0
|
| Gross Unrealized Gains |
26
|
0
|
|
| Gross Unrealized Losses |
0
|
(6)
|
|
| Fair Value |
1,237
|
1,262
|
|
| Agency - Commercial |
|
|
|
| Available-for-sale securities |
|
|
|
| Amortized Cost |
626
|
766
|
541
|
| Gross Unrealized Gains |
14
|
3
|
1
|
| Gross Unrealized Losses |
0
|
(3)
|
(2)
|
| Fair Value |
640
|
766
|
540
|
| Agency - Residential |
|
|
|
| Available-for-sale securities |
|
|
|
| Amortized Cost |
461
|
514
|
1,118
|
| Gross Unrealized Gains |
12
|
2
|
13
|
| Gross Unrealized Losses |
0
|
(2)
|
(1)
|
| Fair Value |
473
|
514
|
1,130
|
| Municipal obligations |
|
|
|
| Available-for-sale securities |
|
|
|
| Amortized Cost |
31
|
14
|
2
|
| Gross Unrealized Gains |
1
|
0
|
0
|
| Gross Unrealized Losses |
0
|
0
|
0
|
| Fair Value |
32
|
14
|
$ 2
|
| Agency - Commercial |
|
|
|
| Held-to-maturity securities |
|
|
|
| Amortized Cost |
635
|
634
|
|
| Gross Unrealized Gains |
12
|
0
|
|
| Gross Unrealized Losses |
0
|
(2)
|
|
| Fair Value |
647
|
632
|
|
| Agency - Residential |
|
|
|
| Held-to-maturity securities |
|
|
|
| Amortized Cost |
576
|
634
|
|
| Gross Unrealized Gains |
14
|
0
|
|
| Gross Unrealized Losses |
0
|
(4)
|
|
| Fair Value |
$ 590
|
$ 630
|
|