Commitments and Contingencies Level 4 (Details) - Annual Purchase Commitments $ in Millions	Dec. 31, 2017 USD ($)
Long-term Purchase Commitment [Line Items]
Total minimum payments	$ 480
Less: Amount representing interest	(33)
Present Value of Minimum Payments	$ 447

If disclosed, the amount of imputed interest necessary to reduce an unconditional purchase obligation to present value on an unrecorded unconditional purchase obligation.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 440
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=77896938&loc=d3e25376-109308

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