Fair Value (Quantitative Information) (Details)	Jun. 30, 2018	Dec. 31, 2017
Interest rate contracts | Minimum | Measurement Input, Swap Yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input	287	200
Interest rate contracts | Minimum | Measurement Input, Repurchase Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input	1	(5)
Interest rate contracts | Maximum | Measurement Input, Swap Yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input	311	300
Interest rate contracts | Maximum | Measurement Input, Repurchase Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input	52	5
Foreign currency exchange rate contracts | Minimum | Measurement Input, Swap Yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input	(27)	(14)
Foreign currency exchange rate contracts | Maximum | Measurement Input, Swap Yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input	309	309
Credit contracts | Minimum | Measurement Input, Credit Spread
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input	97	0
Credit contracts | Maximum | Measurement Input, Credit Spread
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input	100	0
Equity market contracts | Minimum | Measurement Input, Price Volatility
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input	0.1700	0.1100
Equity market contracts | Minimum | Measurement Input, Correlation
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input	0.1000	0.1000
Equity market contracts | Maximum | Measurement Input, Price Volatility
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input	0.3000	0.3100
Equity market contracts | Maximum | Measurement Input, Correlation
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input	0.3000	0.3000
Embedded derivatives direct, assumed and ceded guaranteed minimum benefits | Minimum | Measurement Input, Utilization Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Embedded Derivative Asset (Liability) Net, Measurement Input	0.0000	0.0000
Embedded derivatives direct, assumed and ceded guaranteed minimum benefits | Minimum | Measurement Input, Withdrawal Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Embedded Derivative Asset (Liability) Net, Measurement Input	0.0000	0.0000
Embedded derivatives direct, assumed and ceded guaranteed minimum benefits | Minimum | Measurement Input, Long-Term Equity Volatility
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Embedded Derivative Asset (Liability) Net, Measurement Input	0.0847	0.0825
Embedded derivatives direct, assumed and ceded guaranteed minimum benefits | Minimum | Measurement Input, Counterparty Credit Risk
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Embedded Derivative Asset (Liability) Net, Measurement Input	0.0003	0.0002
Embedded derivatives direct, assumed and ceded guaranteed minimum benefits | Minimum | Durations 1 - 10 | Measurement Input, Lapse Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Embedded Derivative Asset (Liability) Net, Measurement Input	0.0025	0.0025
Embedded derivatives direct, assumed and ceded guaranteed minimum benefits | Minimum | Durations 11 - 20 | Measurement Input, Lapse Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Embedded Derivative Asset (Liability) Net, Measurement Input	0.0200	0.0200
Embedded derivatives direct, assumed and ceded guaranteed minimum benefits | Minimum | Durations 21 - 116 | Measurement Input, Lapse Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Embedded Derivative Asset (Liability) Net, Measurement Input	0.0125	0.0125
Embedded derivatives direct, assumed and ceded guaranteed minimum benefits | Minimum | Ages 0 - 40 | Measurement Input, Mortality Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Embedded Derivative Asset (Liability) Net, Measurement Input	0.0000	0.0000
Embedded derivatives direct, assumed and ceded guaranteed minimum benefits | Minimum | Ages 41 - 60 | Measurement Input, Mortality Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Embedded Derivative Asset (Liability) Net, Measurement Input	0.0003	0.0003
Embedded derivatives direct, assumed and ceded guaranteed minimum benefits | Minimum | Ages 61 - 115 | Measurement Input, Mortality Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Embedded Derivative Asset (Liability) Net, Measurement Input	0.0000	0.0015
Embedded derivatives direct, assumed and ceded guaranteed minimum benefits | Maximum | Measurement Input, Utilization Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Embedded Derivative Asset (Liability) Net, Measurement Input	0.2500	0.2500
Embedded derivatives direct, assumed and ceded guaranteed minimum benefits | Maximum | Measurement Input, Withdrawal Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Embedded Derivative Asset (Liability) Net, Measurement Input	0.2000	0.2000
Embedded derivatives direct, assumed and ceded guaranteed minimum benefits | Maximum | Measurement Input, Long-Term Equity Volatility
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Embedded Derivative Asset (Liability) Net, Measurement Input	0.3300	0.3300
Embedded derivatives direct, assumed and ceded guaranteed minimum benefits | Maximum | Measurement Input, Counterparty Credit Risk
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Embedded Derivative Asset (Liability) Net, Measurement Input	0.0146	0.0132
Embedded derivatives direct, assumed and ceded guaranteed minimum benefits | Maximum | Durations 1 - 10 | Measurement Input, Lapse Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Embedded Derivative Asset (Liability) Net, Measurement Input	1.0000	1.0000
Embedded derivatives direct, assumed and ceded guaranteed minimum benefits | Maximum | Durations 11 - 20 | Measurement Input, Lapse Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Embedded Derivative Asset (Liability) Net, Measurement Input	1.0000	1.0000
Embedded derivatives direct, assumed and ceded guaranteed minimum benefits | Maximum | Durations 21 - 116 | Measurement Input, Lapse Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Embedded Derivative Asset (Liability) Net, Measurement Input	1.0000	1.0000
Embedded derivatives direct, assumed and ceded guaranteed minimum benefits | Maximum | Ages 0 - 40 | Measurement Input, Mortality Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Embedded Derivative Asset (Liability) Net, Measurement Input	0.0021	0.0021
Embedded derivatives direct, assumed and ceded guaranteed minimum benefits | Maximum | Ages 41 - 60 | Measurement Input, Mortality Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Embedded Derivative Asset (Liability) Net, Measurement Input	0.0075	0.0075
Embedded derivatives direct, assumed and ceded guaranteed minimum benefits | Maximum | Ages 61 - 115 | Measurement Input, Mortality Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Embedded Derivative Asset (Liability) Net, Measurement Input	1.0000	1.0000
U.S. corporate and foreign corporate securities | Minimum | Measurement Input, Quoted Price
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt Securities, Available-for-sale, Measurement Input	37	10
U.S. corporate and foreign corporate securities | Minimum | Valuation Technique, Matrix Pricing
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt Securities, Available-for-sale, Measurement Input	87	83
U.S. corporate and foreign corporate securities | Minimum | Valuation Technique, Consensus Pricing Model
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt Securities, Available-for-sale, Measurement Input	96	97
U.S. corporate and foreign corporate securities | Maximum | Measurement Input, Quoted Price
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt Securities, Available-for-sale, Measurement Input	770	443
U.S. corporate and foreign corporate securities | Maximum | Valuation Technique, Matrix Pricing
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt Securities, Available-for-sale, Measurement Input	137	142
U.S. corporate and foreign corporate securities | Maximum | Valuation Technique, Consensus Pricing Model
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt Securities, Available-for-sale, Measurement Input	104	104
U.S. corporate and foreign corporate securities | Weighted Average | Measurement Input, Quoted Price
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt Securities, Available-for-sale, Measurement Input	126	121
U.S. corporate and foreign corporate securities | Weighted Average | Valuation Technique, Matrix Pricing
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt Securities, Available-for-sale, Measurement Input	106	110
U.S. corporate and foreign corporate securities | Weighted Average | Valuation Technique, Consensus Pricing Model
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt Securities, Available-for-sale, Measurement Input	101	101
RMBS | Minimum | Measurement Input, Quoted Price
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt Securities, Available-for-sale, Measurement Input	0	0
RMBS | Maximum | Measurement Input, Quoted Price
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt Securities, Available-for-sale, Measurement Input	109	126
RMBS | Weighted Average | Measurement Input, Quoted Price
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt Securities, Available-for-sale, Measurement Input	95	94
ABS | Minimum | Measurement Input, Quoted Price
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt Securities, Available-for-sale, Measurement Input	3	5
ABS | Minimum | Valuation Technique, Consensus Pricing Model
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt Securities, Available-for-sale, Measurement Input	100	100
ABS | Maximum | Measurement Input, Quoted Price
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt Securities, Available-for-sale, Measurement Input	117	117
ABS | Maximum | Valuation Technique, Consensus Pricing Model
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt Securities, Available-for-sale, Measurement Input	103	103
ABS | Weighted Average | Measurement Input, Quoted Price
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt Securities, Available-for-sale, Measurement Input	100	100
ABS | Weighted Average | Valuation Technique, Consensus Pricing Model
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt Securities, Available-for-sale, Measurement Input	101	100