Fair Value - Separate Accounts Fair Value (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	$ 5,086	$ 4,881
Recurring
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	5,095	4,852
Recurring | Other Payables
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	9
Recurring | Other Receivables
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets		29
Recurring | Cash and cash equivalents
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	219	188
Recurring | Debt securities
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	4,297	4,099
Recurring | Equity securities
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	2	2
Recurring | Common/collective trusts
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	577	563
Recurring | Level 1
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	1,217	1,467
Recurring | Level 1 | Cash and cash equivalents
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	3	2
Recurring | Level 1 | Debt securities
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	1,214	1,465
Recurring | Level 1 | Equity securities
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	0	0
Recurring | Level 1 | Common/collective trusts
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	0	0
Recurring | Level 2
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	3,878	3,385
Recurring | Level 2 | Cash and cash equivalents
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	216	186
Recurring | Level 2 | Debt securities
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	3,083	2,634
Recurring | Level 2 | Equity securities
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	2	2
Recurring | Level 2 | Common/collective trusts
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	577	563
Recurring | Level 3
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	0	0
Recurring | Level 3 | Cash and cash equivalents
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	0	0
Recurring | Level 3 | Debt securities
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	0	0
Recurring | Level 3 | Equity securities
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	0	0
Recurring | Level 3 | Common/collective trusts
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	$ 0	$ 0