Debt Obligations (1.75% Senior Unsecured Notes Due 2023) (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2020	May 31, 2016
Debt Instrument [Line Items]
Decrease in carrying amount	$ 680
1.75% senior unsecured notes due May 19, 2023
Debt Instrument [Line Items]
Stated rate	1.75%
Senior Notes \| 1.75% senior unsecured notes due May 19, 2023
Debt Instrument [Line Items]
Stated rate		1.75%
Decrease in carrying amount	$ 10
Senior Notes \| 1.75% senior unsecured notes due May 19, 2023 \| Maximum
Debt Instrument [Line Items]
Maximum interest rate on debt instrument		3.75%

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 6
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109500613&loc=SL6036836-161870

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28551-108399

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 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant