Fair Value Measurements (excluding Consolidated Investment Entities) - Significant Unobservable Inputs (Details) $ in Billions	12 Months Ended
	Dec. 31, 2017 USD ($) yr	Dec. 31, 2016 USD ($) yr
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Percent of policyholders taking systematic withdrawals	45.00%	40.00%
Percent of policyholders assumed to begin withdrawals	70.00%	85.00%
Fair Value Inputs, Actuarial Assumptions, Benefit Utilization, Percent of Policyholders Utilizing Withdrawals By Age One Hundred	100.00%	100.00%
Account Value	$ 14.0	$ 13.6
Average Expected Delay (in years)	4 years 4 months 24 days	5 years 6 months
Percent of the policies the company assumes will never withdraw		15.00%
Stabilizer / MCG
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Percentage of Plans	100.00%	100.00%
Stabilizer (Investment Only) and MCG Contracts
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Percentage of Plans	92.00%	93.00%
Stabilizer with Recordkeeping Agreements
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Percentage of Plans	8.00%	7.00%
Market Approach Valuation Technique | Investment contract | GMWBL/GMWB/GMAB | Minimum
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Long-term equity implied volatility	15.00%	15.00%
Interest rate implied volatility	0.10%	0.10%
Equity Funds	(13.00%)	(13.00%)
Equity and Fixed Income Funds	(38.00%)	(38.00%)
Interest Rates and Equity Funds	(32.00%)	(32.00%)
Nonperformance risk	0.02%	0.23%
Benefit Utilization	70.00%	85.00%
Partial Withdrawals	0.00%	0.00%
Lapses	10.00%	0.12%
Policyholder Deposits	0.00%	0.00%
Mortality	0.00%	0.00%
Market Approach Valuation Technique | Investment contract | GMWBL/GMWB/GMAB | Maximum
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Long-term equity implied volatility	25.00%	25.00%
Interest rate implied volatility	16.00%	18.00%
Equity Funds	99.00%	99.00%
Equity and Fixed Income Funds	62.00%	62.00%
Interest Rates and Equity Funds	26.00%	16.00%
Nonperformance risk	1.10%	1.30%
Benefit Utilization	100.00%	100.00%
Partial Withdrawals	3.40%	3.40%
Lapses	15.30%	12.40%
Policyholder Deposits	0.00%	0.00%
Mortality	0.00%	0.00%
Market Approach Valuation Technique | Investment contract | FIA | Minimum
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Long-term equity implied volatility	0.00%	0.00%
Interest rate implied volatility	0.00%	0.00%
Equity Funds	0.00%	0.00%
Equity and Fixed Income Funds	0.00%	0.00%
Interest Rates and Equity Funds	0.00%	0.00%
Nonperformance risk	0.02%	0.25%
Benefit Utilization	0.00%	0.00%
Partial Withdrawals	0.50%	0.00%
Lapses	0.00%	0.00%
Policyholder Deposits	0.00%	0.00%
Mortality	0.00%	0.00%
Market Approach Valuation Technique | Investment contract | FIA | Maximum
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Long-term equity implied volatility	0.00%	0.00%
Interest rate implied volatility	0.00%	0.00%
Equity Funds	0.00%	0.00%
Equity and Fixed Income Funds	0.00%	0.00%
Interest Rates and Equity Funds	0.00%	0.00%
Nonperformance risk	1.10%	1.60%
Benefit Utilization	0.00%	0.00%
Partial Withdrawals	7.00%	10.00%
Lapses	56.00%	60.00%
Policyholder Deposits	0.00%	0.00%
Mortality	0.00%	0.00%
Market Approach Valuation Technique | Investment contract | IUL | Minimum
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Long-term equity implied volatility	0.00%	0.00%
Interest rate implied volatility	0.00%	0.00%
Equity Funds	0.00%	0.00%
Equity and Fixed Income Funds	0.00%	0.00%
Interest Rates and Equity Funds	0.00%	0.00%
Nonperformance risk	0.02%	0.23%
Benefit Utilization	0.00%	0.00%
Partial Withdrawals	0.00%	0.00%
Lapses	2.00%	2.00%
Policyholder Deposits	0.00%	0.00%
Mortality	0.00%	0.00%
Market Approach Valuation Technique | Investment contract | IUL | Maximum
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Long-term equity implied volatility	0.00%	0.00%
Interest rate implied volatility	0.00%	0.00%
Equity Funds	0.00%	0.00%
Equity and Fixed Income Funds	0.00%	0.00%
Interest Rates and Equity Funds	0.00%	0.00%
Nonperformance risk	0.54%	0.69%
Benefit Utilization	0.00%	0.00%
Partial Withdrawals	0.00%	0.00%
Lapses	10.00%	10.00%
Policyholder Deposits	0.00%	0.00%
Mortality	0.00%	0.00%
Market Approach Valuation Technique | Derivative liabilities | Stabilizer / MCG | Minimum
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Long-term equity implied volatility	0.00%	0.00%
Interest rate implied volatility	0.10%	0.10%
Equity Funds	0.00%	0.00%
Equity and Fixed Income Funds	0.00%	0.00%
Interest Rates and Equity Funds	0.00%	0.00%
Nonperformance risk	0.02%	0.25%
Benefit Utilization	0.00%	0.00%
Partial Withdrawals	0.00%	0.00%
Lapses	0.00%	0.00%
Policyholder Deposits	0.00%	0.00%
Mortality	0.00%	0.00%
Actuarial Assumptions, Lapses under percent threshold	0.00%	0.00%
Actuarial Assumptions, Policyholder Deposits under percent threshold	0.00%	0.00%
Market Approach Valuation Technique | Derivative liabilities | Stabilizer / MCG | Maximum
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Long-term equity implied volatility	0.00%	0.00%
Interest rate implied volatility	6.30%	7.50%
Equity Funds	0.00%	0.00%
Equity and Fixed Income Funds	0.00%	0.00%
Interest Rates and Equity Funds	0.00%	0.00%
Nonperformance risk	1.10%	1.60%
Benefit Utilization	0.00%	0.00%
Partial Withdrawals	0.00%	0.00%
Lapses	50.00%	50.00%
Policyholder Deposits	50.00%	50.00%
Mortality	0.00%	0.00%
Actuarial Assumptions, Lapses under percent threshold	30.00%	30.00%
Actuarial Assumptions, Policyholder Deposits under percent threshold	25.00%	25.00%
Market Approach Valuation Technique | Derivative liabilities | Stabilizer (Investment Only) and MCG Contracts | Minimum
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Lapses	0.00%	0.00%
Policyholder Deposits	0.00%	0.00%
Actuarial Assumptions, Lapses under percent threshold	0.00%	0.00%
Actuarial Assumptions, Policyholder Deposits under percent threshold	0.00%	0.00%
Market Approach Valuation Technique | Derivative liabilities | Stabilizer (Investment Only) and MCG Contracts | Maximum
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Lapses	25.00%	25.00%
Policyholder Deposits	30.00%	30.00%
Actuarial Assumptions, Lapses under percent threshold	15.00%	15.00%
Actuarial Assumptions, Policyholder Deposits under percent threshold	15.00%	15.00%
Market Approach Valuation Technique | Derivative liabilities | Stabilizer with Recordkeeping Agreements | Minimum
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Lapses	0.00%	0.00%
Policyholder Deposits	0.00%	0.00%
Actuarial Assumptions, Lapses under percent threshold	0.00%	0.00%
Actuarial Assumptions, Policyholder Deposits under percent threshold	0.00%	0.00%
Market Approach Valuation Technique | Derivative liabilities | Stabilizer with Recordkeeping Agreements | Maximum
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Lapses	50.00%	50.00%
Policyholder Deposits	50.00%	50.00%
Actuarial Assumptions, Lapses under percent threshold	30.00%	30.00%
Actuarial Assumptions, Policyholder Deposits under percent threshold	25.00%	25.00%
In the Money
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Account Value	$ 12.5	$ 13.4
In the Money | During Surrender Charge Period | GMWBL/GMWB/GMAB
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Account Value	$ 0.2	$ 2.0
In the Money | During Surrender Charge Period | GMWBL/GMWB/GMAB | Minimum
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Lapses	0.10%	0.10%
In the Money | During Surrender Charge Period | GMWBL/GMWB/GMAB | Maximum
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Lapses	4.80%	4.60%
In the Money | Shock Lapse Period | GMWBL/GMWB/GMAB
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Account Value	$ 1.5	$ 2.8
In the Money | Shock Lapse Period | GMWBL/GMWB/GMAB | Minimum
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Lapses	1.70%	2.40%
In the Money | Shock Lapse Period | GMWBL/GMWB/GMAB | Maximum
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Lapses	13.90%	11.80%
In the Money | After Surrender Charge Period | GMWBL/GMWB/GMAB
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Account Value	$ 10.7	$ 8.7
In the Money | After Surrender Charge Period | GMWBL/GMWB/GMAB | Minimum
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Lapses	0.90%	1.40%
In the Money | After Surrender Charge Period | GMWBL/GMWB/GMAB | Maximum
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Lapses	6.40%	6.80%
Out of the Money
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Account Value	$ 1.5	$ 0.2
Out of the Money | During Surrender Charge Period | GMWBL/GMWB/GMAB
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Account Value	$ 0.1	$ 0.0
Out of the Money | During Surrender Charge Period | GMWBL/GMWB/GMAB | Minimum
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Lapses	0.60%	0.60%
Out of the Money | During Surrender Charge Period | GMWBL/GMWB/GMAB | Maximum
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Lapses	5.20%	4.80%
Out of the Money | Shock Lapse Period | GMWBL/GMWB/GMAB
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Account Value	$ 0.2	$ 0.0
Out of the Money | Shock Lapse Period | GMWBL/GMWB/GMAB | Minimum
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Lapses	13.90%	11.80%
Out of the Money | Shock Lapse Period | GMWBL/GMWB/GMAB | Maximum
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Lapses	15.30%	12.40%
Out of the Money | After Surrender Charge Period | GMWBL/GMWB/GMAB
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Account Value	$ 1.7	$ 0.6
Out of the Money | After Surrender Charge Period | GMWBL/GMWB/GMAB | Minimum
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Lapses	6.40%	6.80%
Out of the Money | After Surrender Charge Period | GMWBL/GMWB/GMAB | Maximum
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Lapses	7.10%	7.10%
Age 60 and under
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Account Value	$ 1.7	$ 1.9
Average Expected Delay (in years)	9 years	9 years 10 months 24 days
Age 60 and under | Minimum
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Attained Age | yr	0	0
Age 60 and under | Maximum
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Attained Age | yr	60	60
Age 60 and under | In the Money
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Account Value	$ 1.5	$ 1.9
Age 60 and under | Out of the Money
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Account Value	0.2	0.0
Age 60-69
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Account Value	$ 5.6	$ 5.8
Average Expected Delay (in years)	3 years 8 months 12 days	4 years 10 months 24 days
Age 60-69 | Minimum
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Attained Age | yr	60	60
Age 60-69 | Maximum
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Attained Age | yr	69	69
Age 60-69 | In the Money
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Account Value	$ 5.0	$ 5.7
Age 60-69 | Out of the Money
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Account Value	0.6	0.1
Age 70 and over
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Account Value	$ 6.7	$ 5.9
Average Expected Delay (in years)	2 years 4 months 24 days	3 years
Age 70 and over | Minimum
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Attained Age | yr	70	70
Age 70 and over | In the Money
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Account Value	$ 6.0	$ 5.8
Age 70 and over | Out of the Money
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Account Value	$ 0.7	$ 0.1