Indebtedness - Schedule of Notes Maturity (Details) - Unsecured Senior Notes $ in Millions	Sep. 30, 2018 USD ($)
Debt Instrument [Line Items]
2018	$ 0
2019	0
2020	0
2021	592
2022	206
Thereafter	1,700
Total	$ 2,498

Face (par) amount of debt instrument at time of issuance.

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-Publisher FASB
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-SubTopic 30
-Section 45
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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section S99
-Paragraph 3
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