Derivative Financial Instruments and Hedging Activities - Derivative Financial Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Derivatives Designated as Hedges [Member] \| Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Notional Amount	$ 3,542	$ 0
Derivative Asset, Fair Value	12	0
Derivatives Designated as Hedges [Member] \| Assets [Member] \| Fair Value Hedges [Member] \| Fair Value, Inputs, Level 2 [Member] \| Interest Rate Swaps [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Notional Amount	0	0
Derivative Asset, Fair Value	0	0
Derivatives Designated as Hedges [Member] \| Assets [Member] \| Cash Flow Hedges [Member] \| Fair Value, Inputs, Level 2 [Member] \| Foreign Currency Swaps [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Notional Amount	0	0
Derivative Asset, Fair Value	0	0
Derivatives Designated as Hedges [Member] \| Assets [Member] \| Cash Flow Hedges [Member] \| Fair Value, Inputs, Level 3 [Member] \| Interest Rate Swaps [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Notional Amount	3,542	0
Derivative Asset, Fair Value	12	0
Derivatives Designated as Hedges [Member] \| Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Notional Amount	9,771	1,000
Derivative Liability, Fair Value	312	6
Derivatives Designated as Hedges [Member] \| Liabilities [Member] \| Fair Value Hedges [Member] \| Fair Value, Inputs, Level 2 [Member] \| Interest Rate Swaps [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Notional Amount	7,700	1,000
Derivative Liability, Fair Value	276	6
Derivatives Designated as Hedges [Member] \| Liabilities [Member] \| Cash Flow Hedges [Member] \| Fair Value, Inputs, Level 2 [Member] \| Foreign Currency Swaps [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Notional Amount	791	0
Derivative Liability, Fair Value	33	0
Derivatives Designated as Hedges [Member] \| Liabilities [Member] \| Cash Flow Hedges [Member] \| Fair Value, Inputs, Level 3 [Member] \| Interest Rate Swaps [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Notional Amount	1,280	0
Derivative Liability, Fair Value	3	0
Derivatives not Designated as Hedges [Member] \| Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Notional Amount	20,712	11,909
Derivative Asset, Fair Value	159	75
Derivatives not Designated as Hedges [Member] \| Assets [Member] \| Fair Value, Inputs, Level 2 [Member] \| Foreign Currency Swaps [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Notional Amount	1,576	1,460
Derivative Asset, Fair Value	78	48
Derivatives not Designated as Hedges [Member] \| Assets [Member] \| Fair Value, Inputs, Level 2 [Member] \| Interest Rate Caps and Floors [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Notional Amount	10,469	6,327
Derivative Asset, Fair Value	26	19
Derivatives not Designated as Hedges [Member] \| Assets [Member] \| Fair Value, Inputs, Level 3 [Member] \| Interest Rate Swaps [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Notional Amount	8,667	4,122
Derivative Asset, Fair Value	55	8
Derivatives not Designated as Hedges [Member] \| Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Notional Amount	20,602	13,933
Derivative Liability, Fair Value	64	43
Derivatives not Designated as Hedges [Member] \| Liabilities [Member] \| Fair Value, Inputs, Level 2 [Member] \| Foreign Currency Swaps [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Notional Amount	119	0
Derivative Liability, Fair Value	2	0
Derivatives not Designated as Hedges [Member] \| Liabilities [Member] \| Fair Value, Inputs, Level 2 [Member] \| Interest Rate Caps and Floors [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Notional Amount	12,146	5,892
Derivative Liability, Fair Value	26	19
Derivatives not Designated as Hedges [Member] \| Liabilities [Member] \| Fair Value, Inputs, Level 3 [Member] \| Interest Rate Swaps [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Notional Amount	8,337	8,041
Derivative Liability, Fair Value	$ 36	$ 24

Nominal or face amount used to calculate payments on the derivative asset.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=64837297&loc=SL5579245-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Notional Amount
-URI http://asc.fasb.org/extlink&oid=6519104

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=64837297&loc=SL5580258-113959

+ Details

Name:	us-gaap_DerivativeAssetNotionalAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Definition

Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 45
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41271-113958

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=73719730&loc=d3e13433-108611

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=73719730&loc=d3e13495-108611

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=51825145&loc=SL20226008-175313

+ Details

Name:	us-gaap_DerivativeAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=51825145&loc=SL20226008-175313

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=73719730&loc=d3e13495-108611

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=73719730&loc=d3e13433-108611

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 45
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41271-113958

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958

+ Details

Name:	us-gaap_DerivativeLiabilities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Nominal or face amount used to calculate payments on the derivative liability.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=64837297&loc=SL5580258-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Notional Amount
-URI http://asc.fasb.org/extlink&oid=6519104

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=64837297&loc=SL5579245-113959

+ Details

Name:	us-gaap_DerivativeLiabilityNotionalAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_DerivativesFairValueLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_HedgingDesignationAxis=us-gaap_DesignatedAsHedgingInstrumentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_OtherAssetsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis=us-gaap_FairValueHedgingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel2Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateSwapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis=us-gaap_CashFlowHedgingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_ForeignExchangeContractMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_OtherLiabilitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_HedgingDesignationAxis=us-gaap_NondesignatedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateContractMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: