Fair Value Measurements - Financial Instruments Not Carried at Fair Value (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, carrying value	$ 70,256	$ 62,307
Assets, fair value	46,781	41,178
Liabilities, carrying value	54,178	49,206
Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value	1,726	1,645
Significant Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value	42,641	37,071
Carrying Amount | Significant Unobservable Inputs (Level 3) | Other policyholder funds and benefits payable
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities, carrying value	772	774
Carrying Amount | Significant Unobservable Inputs (Level 3) | Mortgage loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, carrying value	3,736	3,704
Carrying Amount | Significant Observable Inputs (Level 2) | Senior notes [1]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities, carrying value	3,757	3,589
Carrying Amount | Significant Observable Inputs (Level 2) | Junior subordinated debentures [1]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities, carrying value	1,089	1,089
Fair Value | Significant Unobservable Inputs (Level 3) | Other policyholder funds and benefits payable
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities, fair value	774	775
Fair Value | Significant Unobservable Inputs (Level 3) | Mortgage loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value	3,900	3,746
Fair Value | Significant Observable Inputs (Level 2) | Senior notes [1]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities, fair value	4,416	3,887
Fair Value | Significant Observable Inputs (Level 2) | Junior subordinated debentures [1]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities, fair value	$ 1,122	$ 1,052