Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurements - Investments in Unrealized Loss Position (Details)

v3.19.1
Fair Value Measurements - Investments in Unrealized Loss Position (Details) - Debt Securities [Member] - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Balance, beginning of period $ 170 $ 151
Purchases of investments 7 4
Payments on investments (1) 0
Unrealized gains (losses) on investments recorded in AOCI 2 (3)
Balance, end of period $ 178 $ 152