Fair Value - Separate Accounts Fair Value (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	$ 4,555	$ 4,459
Recurring
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	4,555	4,459
Cash and cash equivalents | Recurring
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	202	145
Debt securities | Recurring
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	3,860	3,813
Equity securities | Recurring
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	2	2
Common/collective trusts | Recurring
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	491	499
Level 1 | Recurring
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	1,277	1,226
Level 1 | Cash and cash equivalents | Recurring
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	4	2
Level 1 | Debt securities | Recurring
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	1,273	1,224
Level 1 | Equity securities | Recurring
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	0	0
Level 1 | Common/collective trusts | Recurring
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	0	0
Level 2 | Recurring
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	3,278	3,233
Level 2 | Cash and cash equivalents | Recurring
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	198	143
Level 2 | Debt securities | Recurring
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	2,587	2,589
Level 2 | Equity securities | Recurring
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	2	2
Level 2 | Common/collective trusts | Recurring
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	491	499
Level 3 | Recurring
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	0	0
Level 3 | Cash and cash equivalents | Recurring
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	0	0
Level 3 | Debt securities | Recurring
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	0	0
Level 3 | Equity securities | Recurring
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	0	0
Level 3 | Common/collective trusts | Recurring
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	$ 0	$ 0