Fair Value (Quantitative Information) (Details) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Interest rate contracts | Minimum | Income Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Swap yield	2.00%	2.00%
Repurchase Rate	(0.05%)	(0.44%)
Interest rate contracts | Maximum | Income Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Swap yield	3.00%	3.00%
Repurchase Rate	0.05%	0.18%
Foreign currency exchange rate contracts | Minimum | Income Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Swap yield	(0.14%)	0.50%
Foreign currency exchange rate contracts | Maximum | Income Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Swap yield	3.09%	3.28%
Credit contracts | Minimum | Income Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Credit spreads	0.00%	0.97%
Credit contracts | Maximum | Income Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Credit spreads	0.00%	0.98%
Equity market contracts | Minimum | Income Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Correlation	10.00%	40.00%
Volatility	11.00%	12.00%
Equity market contracts | Maximum | Income Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Correlation	30.00%	40.00%
Volatility	31.00%	32.00%
Embedded derivatives direct, assumed and ceded guaranteed minimum benefits | Minimum | Income Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Utilization rates	0.00%	0.00%
Withdrawal rates	0.00%	0.00%
Long-term equity volatilities	8.25%	9.95%
Nonperformance risk spread	0.02%	0.04%
Embedded derivatives direct, assumed and ceded guaranteed minimum benefits | Minimum | Income Approach Valuation Technique | Durations 1 - 10
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Lapse Rate	0.25%	0.25%
Embedded derivatives direct, assumed and ceded guaranteed minimum benefits | Minimum | Income Approach Valuation Technique | Durations 11 - 20
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Lapse Rate	2.00%	2.00%
Embedded derivatives direct, assumed and ceded guaranteed minimum benefits | Minimum | Income Approach Valuation Technique | Durations 21 - 116
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Lapse Rate	1.25%	1.25%
Embedded derivatives direct, assumed and ceded guaranteed minimum benefits | Minimum | Income Approach Valuation Technique | Ages 0 - 40
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Mortality Rate	0.00%	0.00%
Embedded derivatives direct, assumed and ceded guaranteed minimum benefits | Minimum | Income Approach Valuation Technique | Ages 41 - 60
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Mortality Rate	0.03%	0.01%
Embedded derivatives direct, assumed and ceded guaranteed minimum benefits | Minimum | Income Approach Valuation Technique | Ages 61 - 115
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Mortality Rate	0.15%	0.04%
Embedded derivatives direct, assumed and ceded guaranteed minimum benefits | Maximum | Income Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Utilization rates	25.00%	25.00%
Withdrawal rates	20.00%	20.00%
Long-term equity volatilities	33.00%	33.00%
Nonperformance risk spread	1.32%	1.70%
Embedded derivatives direct, assumed and ceded guaranteed minimum benefits | Maximum | Income Approach Valuation Technique | Durations 1 - 10
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Lapse Rate	100.00%	100.00%
Embedded derivatives direct, assumed and ceded guaranteed minimum benefits | Maximum | Income Approach Valuation Technique | Durations 11 - 20
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Lapse Rate	100.00%	100.00%
Embedded derivatives direct, assumed and ceded guaranteed minimum benefits | Maximum | Income Approach Valuation Technique | Durations 21 - 116
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Lapse Rate	100.00%	100.00%
Embedded derivatives direct, assumed and ceded guaranteed minimum benefits | Maximum | Income Approach Valuation Technique | Ages 0 - 40
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Mortality Rate	0.21%	0.21%
Embedded derivatives direct, assumed and ceded guaranteed minimum benefits | Maximum | Income Approach Valuation Technique | Ages 41 - 60
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Mortality Rate	0.75%	0.78%
Embedded derivatives direct, assumed and ceded guaranteed minimum benefits | Maximum | Income Approach Valuation Technique | Ages 61 - 115
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Mortality Rate	100.00%	100.00%
U.S. corporate and foreign corporate securities | Minimum | Market Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Matrix Pricing - Offered quotes	$ 83	$ 18
Offered quotes	97	37
Quoted prices	10	6
U.S. corporate and foreign corporate securities | Maximum | Market Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Matrix Pricing - Offered quotes	142	138
Offered quotes	104	120
Quoted prices	443	700
U.S. corporate and foreign corporate securities | Weighted Average | Market Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Matrix Pricing - Offered quotes	110	106
Offered quotes	101	102
Quoted prices	121	116
RMBS | Minimum | Market Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Quoted prices	0	19
RMBS | Maximum | Market Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Quoted prices	126	137
RMBS | Weighted Average | Market Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Quoted prices	94	91
ABS | Minimum | Market Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Offered quotes	100	96
Quoted prices	5	5
ABS | Maximum | Market Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Offered quotes	103	102
Quoted prices	117	106
ABS | Weighted Average | Market Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Offered quotes	100	100
Quoted prices	$ 100	$ 99