Loans Mortgages With Potential Concentration of Credit Risk (Details) - USD ($) $ in Millions		Dec. 31, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair Value, Concentration of Risk, Loans Receivable		$ 10,322	$ 10,476
Residential Mortgage Interest Only Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair Value, Concentration of Risk, Loans Receivable	[1]	1,124	2,110
Residential Mortgage Interest Only Loans [Member] | Mortgages With Mortgage Insurance or With LTV Ratio Less Than or Equal to 80% [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair Value, Concentration of Risk, Loans Receivable	[1]	845	1,563
Residential Mortgage Interest Only Loans [Member] | Mortgages With No Mortgage Insurance and With LTV Ratio Greater Than 80% [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair Value, Concentration of Risk, Loans Receivable	[1]	279	547
Residential Mortgage Amortizing Loans [Member] | Mortgages With LTV Ratio Greater Than 80% and/or second liens [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair Value, Concentration of Risk, Loans Receivable	[2]	$ 9,198	$ 8,366

[1] Comprised of first and/or second liens, primarily with an initial 10 year interest only period.

[2] Comprised of loans with no MI.