Pledged Assets (Assets Pledged from Counterparties) (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Offsetting Assets and Liabilities [Line Items]
Federal Home Loan Bank Stock	$ 126	$ 150
Available-for-sale Securities Pledged as Collateral	44,089	48,380
Obligation to Return Securities Borrowed Under Reverse Repurchase Agreements at Fair Value	5,424	1,696
Restricted Cash and Cash Equivalents	681	1,281
US Treasury Securities [Member]
Offsetting Assets and Liabilities [Line Items]
Available-for-sale Securities Pledged as Collateral	45	25
US Treasury Securities [Member] | Assets Pledged to Us [Member]
Offsetting Assets and Liabilities [Line Items]
Available-for-sale Securities Pledged as Collateral	5,400	1,700
Derivative [Member]
Offsetting Assets and Liabilities [Line Items]
Available-for-sale Securities Pledged as Collateral	684	148
Restricted Cash and Cash Equivalents	666	1,226
Derivative [Member] | US Treasury Securities [Member]
Offsetting Assets and Liabilities [Line Items]
Available-for-sale Securities Pledged as Collateral	$ 0	$ 0