Income Taxes - Reconciliation of income tax rate (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Total costs and expenses	$ 6,089	$ 2,628	$ 4,549
Statutory federal income tax rate on income from operations	1,279	552	1,592
Tax credits	(33)	(34)	(59)
Share-based payments	(24)	(16)	(63)
Tax-exempt income	(27)	(24)	(32)
State income taxes	41	27	21
Tax Legislation benefit	0	(29)	(509)
Non-deductible goodwill impairment	0	0	44
Other	6	(8)	1
Total income tax expense	$ 1,242	$ 468	$ 995
Effective Income Tax Rate, Continuing Operations, Tax Rate Reconciliation
Statutory federal income tax rate on income from operations	21.00%	21.00%	35.00%
Tax credits	(0.50%)	(1.30%)	(1.30%)
Share-based payments	(0.40%)	(0.60%)	(1.40%)
Tax-exempt income	(0.40%)	(0.90%)	(0.70%)
State income taxes	0.70%	1.00%	0.50%
Tax Legislation benefit	0.00%	(1.10%)	(11.20%)
Non-deductible goodwill impairment	0.00%	0.00%	1.00%
Other	0.00%	(0.30%)	0.00%
Effective income tax rate on income from operations	20.40%	17.80%	21.90%