Federal Home Loan Bank Advances (Schedule of FHLB, Advances, Maturity Summary) (Details) - USD ($) $ in Millions |
Jun. 30, 2016 |
Dec. 31, 2015 |
Dec. 31, 2014 |
Dec. 31, 2013 |
|---|---|---|---|---|
| Advances from Federal Home Loan Banks [Abstract] | ||||
| 2016 | $ 1,194 | $ 2,291 | ||
| 2017 | 50 | 50 | ||
| 2018 | 125 | 125 | ||
| 2019 | 0 | 0 | ||
| Thereafter | 1,277 | 1,075 | ||
| Total | $ 2,646 | $ 3,541 | $ 514 | $ 988 |