Fair Value Measurements (excluding Consolidated Investment Entities) - Significant Unobservable Inputs (Details) - IUL - Investment contract - Market Approach Valuation Technique	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Weighted Average
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Interest rate implied volatility	0.00%
Nonperformance risk	0.36%
Lapses	6.00%
Mortality	0.00%
Maximum
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Interest rate implied volatility	0.00%	0.00%
Nonperformance risk	0.66%	0.42%
Lapses	10.00%	10.00%
Mortality	0.00%	0.00%
Minimum
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Interest rate implied volatility	0.00%	0.00%
Nonperformance risk	0.22%	0.22%
Lapses	2.00%	2.00%
Mortality	0.00%	0.00%