Fair Value - Separate Accounts Fair Value (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	$ 4,793	$ 4,459
Recurring
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	4,793	4,459
Cash and cash equivalents | Recurring
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	74	145
Debt securities | Recurring
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	4,114	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	603	499
Level 1 | Recurring
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	1,540	1,226
Level 1 | Cash and cash equivalents | Recurring
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	2	2
Level 1 | Debt securities | Recurring
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	1,538	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	3,253	3,233
Level 2 | Cash and cash equivalents | Recurring
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	72	143
Level 2 | Debt securities | Recurring
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	2,576	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	603	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