Fair Value - Separate Accounts Fair Value (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	$ 4,459	$ 3,884
Recurring
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	4,459	3,884
Recurring | Cash and cash equivalents
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	145	191
Recurring | Debt securities
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	3,813	3,286
Recurring | Equity securities
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	2	3
Recurring | Common/collective trusts
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	499	404
Recurring | Level 1
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	1,226	784
Recurring | Level 1 | Cash and cash equivalents
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	2	2
Recurring | Level 1 | Debt securities
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	1,224	782
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	3,233	3,096
Recurring | Level 2 | Cash and cash equivalents
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	143	189
Recurring | Level 2 | Debt securities
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	2,589	2,500
Recurring | Level 2 | Equity securities
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	2	3
Recurring | Level 2 | Common/collective trusts
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	499	404
Recurring | Level 3
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	0	4
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	4
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