Federal Home Loan Bank Stock (Details) - USD ($) $ in Millions |
6 Months Ended | 12 Months Ended | |||
|---|---|---|---|---|---|
Jun. 30, 2016 |
Jun. 30, 2015 |
Dec. 31, 2015 |
Dec. 31, 2014 |
Dec. 31, 2013 |
|
| Federal Home Loan Bank Stock [Abstract] | |||||
| Federal Home Loan Bank stock | $ 172 | $ 170 | $ 155 | ||
| Federal Home Loan Bank stock, minimum investment requirement, percentage of unpaid principal of mortgage loans, home purchase contracts and similar obligations | 1.00% | ||||
| Federal Home Loan Bank minimum percentage of advances required held | 4.50% | ||||
| Federal Home Loan Required Stock Purchases | $ 57 | ||||
| Proceeds from redemption of Federal Home Loan Bank stock | $ (2) | $ 42 | 42 | 54 | $ 92 |
| Dividend income | $ 6 | $ 9 | $ 11 | ||