Derivative Financial Instruments (Master Netting Schedule) (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Derivative Asset [Abstract]
Gross Amounts Not Offset in the Statement of Financial Condition, Cash Collateral	$ 13	$ 74
Derivative Liability [Abstract]
Gross Amounts Not Offset in the Statement of Financial Condition, Cash Collateral		54
Central Counterparty Clearing House
Derivative Liability [Abstract]
Collateral Already Posted, Aggregate Fair Value	15
Derivatives designated as hedging instruments \| Interest rate swaps on FHLB advances
Derivative Asset [Abstract]
Gross Amount	2	20
Gross Amounts Netted in the Statement of Financial Position	0	1
Net Amount Presented in the Statement of Financial Position	2	19
Gross Amounts Not Offset in the Statement of Financial Condition, Financial Instruments	0	0
Gross Amounts Not Offset in the Statement of Financial Condition, Cash Collateral		0
Derivative Liability [Abstract]
Gross Amount		1
Gross Amounts Netted in the Statement of Financial Position		1
Net Amount Presented in the Statement of Financial Position		0
Gross Amounts Not Offset in the Statement of Financial Condition, Financial Instruments		0
Gross Amounts Not Offset in the Statement of Financial Condition, Cash Collateral	27	33
Derivatives not designated as hedging instruments
Derivative Asset [Abstract]
Gross Amount	39	80
Gross Amounts Netted in the Statement of Financial Position	0	0
Net Amount Presented in the Statement of Financial Position	39	80
Gross Amounts Not Offset in the Statement of Financial Condition, Financial Instruments	0	0
Gross Amounts Not Offset in the Statement of Financial Condition, Cash Collateral	13	74
Derivative Liability [Abstract]
Gross Amount	7	48
Gross Amounts Netted in the Statement of Financial Position	0	0
Net Amount Presented in the Statement of Financial Position	7	48
Gross Amounts Not Offset in the Statement of Financial Condition, Financial Instruments	0	0
Gross Amounts Not Offset in the Statement of Financial Condition, Cash Collateral	18	21
Derivatives not designated as hedging instruments \| Mortgage backed securities forwards
Derivative Asset [Abstract]
Gross Amount	24	43
Gross Amounts Netted in the Statement of Financial Position	0	0
Net Amount Presented in the Statement of Financial Position	24	43
Gross Amounts Not Offset in the Statement of Financial Condition, Financial Instruments	0	0
Gross Amounts Not Offset in the Statement of Financial Condition, Cash Collateral	2	44
Derivative Liability [Abstract]
Gross Amount	4	11
Gross Amounts Netted in the Statement of Financial Position	0	0
Net Amount Presented in the Statement of Financial Position	4	11
Gross Amounts Not Offset in the Statement of Financial Condition, Financial Instruments	0	0
Gross Amounts Not Offset in the Statement of Financial Condition, Cash Collateral	11	0
Derivatives not designated as hedging instruments \| Interest rate swaps and swaptions
Derivative Asset [Abstract]
Gross Amount	15	35
Gross Amounts Netted in the Statement of Financial Position	0	0
Net Amount Presented in the Statement of Financial Position	15	35
Gross Amounts Not Offset in the Statement of Financial Condition, Financial Instruments	0	0
Gross Amounts Not Offset in the Statement of Financial Condition, Cash Collateral	11	30
Derivative Liability [Abstract]
Gross Amount	2	37
Gross Amounts Netted in the Statement of Financial Position	0	0
Net Amount Presented in the Statement of Financial Position	2	37
Gross Amounts Not Offset in the Statement of Financial Condition, Financial Instruments	0	0
Gross Amounts Not Offset in the Statement of Financial Condition, Cash Collateral	4	20
Derivatives not designated as hedging instruments \| Futures
Derivative Asset [Abstract]
Gross Amount		2
Gross Amounts Netted in the Statement of Financial Position		0
Net Amount Presented in the Statement of Financial Position		2
Gross Amounts Not Offset in the Statement of Financial Condition, Financial Instruments		0
Gross Amounts Not Offset in the Statement of Financial Condition, Cash Collateral		0
Derivative Liability [Abstract]
Gross Amount	1	0
Gross Amounts Netted in the Statement of Financial Position	0	0
Net Amount Presented in the Statement of Financial Position	1	0
Gross Amounts Not Offset in the Statement of Financial Condition, Financial Instruments	0	0
Gross Amounts Not Offset in the Statement of Financial Condition, Cash Collateral	$ 3	$ 1

The aggregate fair value of assets that are already posted, at the end of the reporting period, as collateral for derivative instruments with credit-risk-related contingent features.

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