Derivatives and Hedging Activities (Fair Value of Derivative Instruments) (Details) - USD ($) $ in Millions		Jun. 30, 2019	Dec. 31, 2018
Derivative [Line Items]
Variation Margin for Daily Settled Contracts, Net		$ 692	$ 21
Cash collateral posted		411	433
Cash collateral received		22	9
Total notional amount of derivatives before netting and collateral adjustments		64,357	59,518
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement		67	36
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement		97	163
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset	[1],[2]	301	278
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset	[1],[2]	(88)	(146)
Derivative assets		368	314
Derivative liabilities		9	17
Designated as Hedging Instrument [Member] | Interest rate swaps [Member]
Derivative [Line Items]
Total notional amount of derivatives before netting and collateral adjustments	[3]	56,670	50,427
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	[3]	60	32
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement	[3]	93	151
Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Total notional amount of derivatives before netting and collateral adjustments		7,687	9,091
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement		7	4
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement		4	12
Not Designated as Hedging Instrument [Member] | Interest rate swaps [Member]
Derivative [Line Items]
Total notional amount of derivatives before netting and collateral adjustments	[3]	604	1,008
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	[3]	5	3
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement	[3]	2	11
Not Designated as Hedging Instrument [Member] | Interest rate caps or floors [Member]
Derivative [Line Items]
Total notional amount of derivatives before netting and collateral adjustments		7,083	8,083
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement		2	1
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement		$ 2	$ 1

[1] Amounts represent the application of the netting requirements that allow the Bank to settle positive and negative positions, and also cash collateral and related accrued interest held or placed with the same clearing agents and/or counterparty. Cash collateral posted and related accrued interest was $411 and $433 as of June 30, 2019 and December 31, 2018, respectively. Cash collateral received and related accrued interest was $22 and $9 as of June 30, 2019 and December 31, 2018, respectively.

[2] Amounts represent the application of the netting requirements that allow the Bank to settle positive and negative positions, and also cash collateral and related accrued interest held or placed with the same clearing agents and/or counterparty.

[3] Includes variation margin for daily settled contracts of $692 and $21 as of June 30, 2019 and December 31, 2018, respectively.