Fair values as of the balance sheet date of the net amount of all assets and liabilities resulting from contracts that meet the criteria of being accounted for as derivative instruments.

Reference 1: 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

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Measure of dispersion, in percentage terms (for instance, the standard deviation or variance), for a given stock price.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)
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Percentage of adjustment to the observed price for a similar asset or liability when an identical transaction does not exist, used as an input to measure fair value.

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Fair Value Measurements - Significant Unobservable Inputs Freestanding Derivatives (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Jun. 30, 2018	Dec. 31, 2017
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Comparability Adjustments	0.00%	0.00%
Significant Unobservable Inputs (Level 3) \| Interest rate swaptions [2] \| Long
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Derivative Assets (Liabilities), at Fair Value, Net	$ 2	$ 2	$ 1
Significant Unobservable Inputs (Level 3) \| Interest rate swaptions [2] \| Minimum \| Long
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Assumptions, Expected Volatility Rate		3.00%	2.00%
Significant Unobservable Inputs (Level 3) \| Interest rate swaptions [2] \| Maximum \| Long
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Assumptions, Expected Volatility Rate		3.00%	2.00%
Significant Unobservable Inputs (Level 3) \| Equity Options
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Derivative Assets (Liabilities), at Fair Value, Net	$ 1	$ 1	$ 1
Significant Unobservable Inputs (Level 3) \| Equity Options \| Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Assumptions, Expected Volatility Rate		16.00%	18.00%
Significant Unobservable Inputs (Level 3) \| Equity Options \| Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Assumptions, Expected Volatility Rate		24.00%	22.00%