Fair Value Measurements Level 4 Significant Unobservable Inputs - Freestanding Derivatives (Details) $ in Millions	5 Months Ended	7 Months Ended	12 Months Ended
	May 31, 2018 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value, Assets, Level 2 to Level 1 Transfers, Amount				$ 0
Fair value assets level 2 to level 1 transfer amount	$ 0	$ 0
Fair value assets level 1 to level 2 Transfer amount	$ 283	171		773
Fair Value, Inputs, Level 3 [Member] | Interest Rate Swap [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Assets (Liabilities), at Fair Value, Net		(27)	$ (27)	$ (29)
Fair Value Measurements, Sensitivity Analysis, Description			Decrease	Decrease
Fair Value, Inputs, Level 3 [Member] | Variance Swap [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Assets (Liabilities), at Fair Value, Net		(26)	$ (26)	$ (26)
Fair Value Measurements, Sensitivity Analysis, Description			Increase	Increase
Fair Value, Inputs, Level 3 [Member] | Equity Option [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Assets (Liabilities), at Fair Value, Net		250	$ 250	$ 29
Fair Value Measurements, Sensitivity Analysis, Description			Increase	Increase
Fair Value, Inputs, Level 3 [Member] | Swap [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Assets (Liabilities), at Fair Value, Net		71	$ 71	$ 59
Fair Value Measurements, Sensitivity Analysis, Description			Increase	Increase
Equity Option [Member] | Fair Value, Inputs, Level 3 [Member] | Hedge Funds, Equity [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Assets (Liabilities), at Fair Value, Net		$ (1)	$ (1)	$ 1
Fair Value Measurements, Valuation Processes, Description			Option model	Option model
Fair Value Measurements, Sensitivity Analysis, Description			Increase	Increase
Equity Option [Member] | Fair Value, Inputs, Level 3 [Member] | Minimum [Member] | Hedge Funds, Equity [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input		0.30	0.30	0.27
Equity Option [Member] | Fair Value, Inputs, Level 3 [Member] | Maximum [Member] | Hedge Funds, Equity [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input		0.32	0.32	0.30
Interest Rate Swaption [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Assets (Liabilities), at Fair Value, Net		$ 1	$ 1
Fair Value Measurements, Sensitivity Analysis, Description			Increase
Measurement Input, Discount Rate [Member] | Fair Value, Inputs, Level 3 [Member] | Interest Rate Swap [Member] | Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input		0.03	0.03	0.02
Measurement Input, Discount Rate [Member] | Fair Value, Inputs, Level 3 [Member] | Interest Rate Swap [Member] | Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input		0.03	0.03	0.03
Measurement Input, Price Volatility [Member] | Fair Value, Inputs, Level 3 [Member] | Variance Swap [Member] | Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input		0.22	0.22	0.19
Measurement Input, Price Volatility [Member] | Fair Value, Inputs, Level 3 [Member] | Variance Swap [Member] | Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input		0.22	0.22	0.19
Measurement Input, Price Volatility [Member] | Fair Value, Inputs, Level 3 [Member] | Equity Option [Member] | Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input		0.17	0.17	0.18
Measurement Input, Price Volatility [Member] | Fair Value, Inputs, Level 3 [Member] | Equity Option [Member] | Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input		0.30	0.30	0.31
Measurement Input, Price Volatility [Member] | Fair Value, Inputs, Level 3 [Member] | Swap [Member] | Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input		0.18	0.18	0.07
Measurement Input, Price Volatility [Member] | Fair Value, Inputs, Level 3 [Member] | Swap [Member] | Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input		0.30	0.30	0.30
Measurement Input, Price Volatility [Member] | Interest Rate Swaption [Member] | Fair Value, Inputs, Level 3 [Member] | Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input		0.03	0.03
Measurement Input, Price Volatility [Member] | Interest Rate Swaption [Member] | Fair Value, Inputs, Level 3 [Member] | Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input		0.03	0.03
Valuation Technique, Discounted Cash Flow [Member] | Fair Value, Inputs, Level 3 [Member] | Interest Rate Swap [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value Measurements, Valuation Processes, Description			Discounted cash flows	Discounted cash flows
Valuation Technique, Discounted Cash Flow [Member] | Fair Value, Inputs, Level 3 [Member] | Swap [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value Measurements, Valuation Processes, Description			Discounted cash flows	Discounted cash flows
Valuation Technique, Discounted Cash Flow [Member] | Interest Rate Swaption [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value Measurements, Valuation Processes, Description			Option model
Valuation Technique, Option Pricing Model [Member] | Fair Value, Inputs, Level 3 [Member] | Variance Swap [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value Measurements, Valuation Processes, Description			Option model	Option model
Valuation Technique, Option Pricing Model [Member] | Fair Value, Inputs, Level 3 [Member] | Equity Option [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value Measurements, Valuation Processes, Description			Option model	Option model