Loans to and Investments in Associated Companies (Berkadia, Narrative) (Details) - USD ($)	12 Months Ended
Dec. 31, 2009	May 31, 2020
Berkadia
Investments In Associated Companies [Line Items]
Surety policy issued		$ 1,500,000,000
Reimbursement of losses incurred, maximum percentage		50.00%
Commercial paper		$ 1,470,000,000
Berkadia
Investments In Associated Companies [Line Items]
Capital contributed	$ 217,200,000
Equity method investment, ownership percentage		50.00%
Percentage of profits received from joint venture		45.00%
Reimbursement of losses incurred, maximum percentage		50.00%

Carrying value as of the balance sheet date of short-term borrowings using unsecured obligations issued by banks, corporations and other borrowers to investors. The maturities of these money market securities generally do not exceed 270 days.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(13)(2))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(19)(a)(3))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

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