Tax Credits for US Citizen Residing in Japan

I'm a US citizen, but I'm a permanent resident of Japan.  As such, I must report my worldwide income to BOTH countries for taxation.  I have tried and tried to find clear, simple written explanations of which country I should pay income tax to first for certain forms of income, and which country will grant me a tax credit.  And if I ask around, I get conflicting answers.   Why does this have to be so confusing?

Q:  Which country has to allow for a tax credit?
Could someone please give me a clear, simple answer for each the following:

1. US Social Security Retirement Benefits
2. Japanese Pension (Nenkin) Retirement Benefits
3. US-source Bank Interest
4. Japanese-source Bank Interest
5. US-source Dividends from Stock or Mutual Funds
6. US-source Capital Gains Distributions from Mutual Funds
7. US-source After-tax Retirement Annuity (ATRA) Income

8. US-source Government (Federal or State) Pension Income

9. US-source IRA and 401k Income 

 

I'd really appreciate answers, and I'm sure they'd be helpful to others, as well.

Thank you.