Fair Value Measurements - Financial Instruments Not Carried at Fair Value (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, carrying value	$ 63,324	$ 62,307
Assets, fair value	42,341	41,178
Liabilities, carrying value	48,984	49,206
Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value	1,508	1,645
Significant Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value	38,062	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	751	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	3,637	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	3,177	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	753	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	3,702	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	3,619	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	$ 1,109	$ 1,052