Fair Value Measurements - Investments and Derivatives (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Assets:
Corporate bonds	$ 0	$ 1
Common stock and equivalents	25	19
Recurring | Corporate bonds
Assets:
Corporate bonds		1
Recurring | Common stock and equivalents
Assets:
Common stock and equivalents	25	19
Recurring | Foreign exchange derivative contracts
Assets:
Foreign exchange derivative contracts	4	5
Liabilities:
Foreign exchange derivative contracts	5	4
Level 1 | Recurring | Corporate bonds
Assets:
Corporate bonds		1
Level 1 | Recurring | Common stock and equivalents
Assets:
Common stock and equivalents	25	19
Level 1 | Recurring | Foreign exchange derivative contracts
Assets:
Foreign exchange derivative contracts	0	0
Liabilities:
Foreign exchange derivative contracts	0	0
Level 2 | Recurring | Corporate bonds
Assets:
Corporate bonds		0
Level 2 | Recurring | Common stock and equivalents
Assets:
Common stock and equivalents	0	0
Level 2 | Recurring | Foreign exchange derivative contracts
Assets:
Foreign exchange derivative contracts	4	5
Liabilities:
Foreign exchange derivative contracts	$ 5	$ 4