Fair Value, Assets and Liabilities Measured on Recurring Basis Level 3 Reconciliation (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Equity securities [Member]
Assets:
Balance, beginning of period	$ 6,381	$ 5,219	$ 5,468	$ 5,203
Net gains (losses) included in net income	724	585	1,650	693
Net gains (losses) included in other comprehensive income	0	0	0	0
Purchases, sales, issuances and settlements, net	0	0	(1)	(96)
Transfers into Level 3	5	6	5	10
Transfers out of Level 3	0	(4)	(12)	(4)
Balance, end of period	7,110	5,806	7,110	5,806
Net unrealized gains (losses) included in income related to assets and liabilities held at period end	724	586	1,650	687
Nonmarketable equity securities [Member]
Assets:
Balance, beginning of period	6,381	5,219	5,468	5,203
Net gains (losses) included in net income	724	585	1,650	693
Net gains (losses) included in other comprehensive income	0	0	0	0
Purchases, sales, issuances and settlements, net	0	0	(1)	(96)
Transfers into Level 3	5	6	5	10
Transfers out of Level 3	0	(4)	(12)	(4)
Balance, end of period	7,110	5,806	7,110	5,806
Net unrealized gains (losses) included in income related to assets and liabilities held at period end	724	586	1,650	687
Trading debt securities [Member] | Debt securities [Member]
Assets:
Balance, beginning of period	331	371	290	407
Net gains (losses) included in net income	(2)	(7)	(4)	(6)
Net gains (losses) included in other comprehensive income	0	0	0	0
Purchases, sales, issuances and settlements, net	(21)	(16)	22	(53)
Transfers into Level 3	0	0	1	0
Transfers out of Level 3	(1)	(1)	(2)	(1)
Balance, end of period	307	347	307	347
Net unrealized gains (losses) included in income related to assets and liabilities held at period end	(5)	(7)	(1)	0
Trading debt securities [Member] | Securities of U.S. states and political subdivisions [Member]
Assets:
Balance, beginning of period	0	3	3	3
Net gains (losses) included in net income	0	0	0	0
Net gains (losses) included in other comprehensive income	0	0	0	0
Purchases, sales, issuances and settlements, net	0	0	(2)	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	(1)	0
Balance, end of period	0	3	0	3
Net unrealized gains (losses) included in income related to assets and liabilities held at period end	0	0	0	0
Trading debt securities [Member] | Corporate debt securities [Member]
Assets:
Balance, beginning of period	41	34	34	31
Net gains (losses) included in net income	1	0	3	0
Net gains (losses) included in other comprehensive income	0	0	0	0
Purchases, sales, issuances and settlements, net	3	3	7	6
Transfers into Level 3	0	0	1	0
Transfers out of Level 3	(1)	(1)	(1)	(1)
Balance, end of period	44	36	44	36
Net unrealized gains (losses) included in income related to assets and liabilities held at period end	1	1	3	0
Trading debt securities [Member] | Collateralized loan obligations [Member]
Assets:
Balance, beginning of period	275	316	237	354
Net gains (losses) included in net income	(2)	(6)	(5)	(4)
Net gains (losses) included in other comprehensive income	0	0	0	0
Purchases, sales, issuances and settlements, net	(24)	(19)	17	(59)
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Balance, end of period	249	291	249	291
Net unrealized gains (losses) included in income related to assets and liabilities held at period end	(6)	(8)	(4)	0
Trading debt securities [Member] | Other trading debt securities [Member]
Assets:
Balance, beginning of period	15	18	16	19
Net gains (losses) included in net income	(1)	(1)	(2)	(2)
Net gains (losses) included in other comprehensive income	0	0	0	0
Purchases, sales, issuances and settlements, net	0	0	0	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Balance, end of period	14	17	14	17
Net unrealized gains (losses) included in income related to assets and liabilities held at period end	0	0	0	0
Available-for-sale securities [Member] | Debt securities [Member]
Assets:
Balance, beginning of period	2,005	2,641	2,044	2,994
Net gains (losses) included in net income	8	8	15	27
Net gains (losses) included in other comprehensive income	(5)	8	(3)	44
Purchases, sales, issuances and settlements, net	(154)	(154)	(202)	(293)
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	(49)	(10)	(49)	(279)
Balance, end of period	1,805	2,493	1,805	2,493
Net unrealized gains (losses) included in income related to assets and liabilities held at period end	0	0	0	0
Available-for-sale securities [Member] | Securities of U.S. states and political subdivisions [Member]
Assets:
Balance, beginning of period	470	617	444	925
Net gains (losses) included in net income	1	1	1	5
Net gains (losses) included in other comprehensive income	2	0	5	(2)
Purchases, sales, issuances and settlements, net	(33)	(49)	(10)	(90)
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	(49)	(10)	(49)	(279)
Balance, end of period	391	559	391	559
Net unrealized gains (losses) included in income related to assets and liabilities held at period end	0	0	0	0
Available-for-sale securities [Member] | Mortgage-backed securities [Member]
Assets:
Balance, beginning of period	41	68	41	76
Net gains (losses) included in net income	0	0	0	1
Net gains (losses) included in other comprehensive income	0	(2)	0	(3)
Purchases, sales, issuances and settlements, net	0	(13)	0	(21)
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Balance, end of period	41	53	41	53
Net unrealized gains (losses) included in income related to assets and liabilities held at period end	0	0	0	0
Available-for-sale securities [Member] | Residential [Member]
Assets:
Balance, beginning of period	0	1	0	1
Net gains (losses) included in net income	0	0	0	0
Net gains (losses) included in other comprehensive income	0	(1)	0	(1)
Purchases, sales, issuances and settlements, net	0	0	0	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Balance, end of period	0	0	0	0
Net unrealized gains (losses) included in income related to assets and liabilities held at period end	0	0	0	0
Available-for-sale securities [Member] | Commercial [Member]
Assets:
Balance, beginning of period	41	67	41	75
Net gains (losses) included in net income	0	0	0	1
Net gains (losses) included in other comprehensive income	0	(1)	0	(2)
Purchases, sales, issuances and settlements, net	0	(13)	0	(21)
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Balance, end of period	41	53	41	53
Net unrealized gains (losses) included in income related to assets and liabilities held at period end	0	0	0	0
Available-for-sale securities [Member] | Corporate debt securities [Member]
Assets:
Balance, beginning of period	377	410	370	407
Net gains (losses) included in net income	0	1	1	2
Net gains (losses) included in other comprehensive income	(1)	1	3	4
Purchases, sales, issuances and settlements, net	7	31	9	30
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Balance, end of period	383	443	383	443
Net unrealized gains (losses) included in income related to assets and liabilities held at period end	0	0	0	0
Available-for-sale securities [Member] | Collateralized loan obligations [Member]
Assets:
Balance, beginning of period	755	1,045	800	1,020
Net gains (losses) included in net income	7	6	13	11
Net gains (losses) included in other comprehensive income	(6)	10	(10)	53
Purchases, sales, issuances and settlements, net	(107)	(24)	(154)	(47)
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Balance, end of period	649	1,037	649	1,037
Net unrealized gains (losses) included in income related to assets and liabilities held at period end	0	0	0	0
Available-for-sale securities [Member] | Asset-backed securities [Member]
Assets:
Balance, beginning of period	362	501	389	566
Net gains (losses) included in net income	0	0	0	8
Net gains (losses) included in other comprehensive income	0	(1)	(1)	(8)
Purchases, sales, issuances and settlements, net	(21)	(99)	(47)	(165)
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Balance, end of period	341	401	341	401
Net unrealized gains (losses) included in income related to assets and liabilities held at period end	0	0	0	0
Available-for-sale securities [Member] | Other asset-backed securities [Member]
Assets:
Balance, beginning of period	362	501	389	566
Net gains (losses) included in net income	0	0	0	8
Net gains (losses) included in other comprehensive income	0	(1)	(1)	(8)
Purchases, sales, issuances and settlements, net	(21)	(99)	(47)	(165)
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Balance, end of period	341	401	341	401
Net unrealized gains (losses) included in income related to assets and liabilities held at period end	0	0	0	0
Mortgage loans held for sale [Member]
Assets:
Balance, beginning of period	998	950	997	998
Net gains (losses) included in net income	37	(11)	52	(34)
Net gains (losses) included in other comprehensive income	0	0	0	0
Purchases, sales, issuances and settlements, net	(22)	25	(88)	(12)
Transfers into Level 3	104	25	160	40
Transfers out of Level 3	(2)	(3)	(6)	(6)
Balance, end of period	1,115	986	1,115	986
Net unrealized gains (losses) included in income related to assets and liabilities held at period end	39	(11)	54	(32)
Loans held for sale [Member]
Assets:
Balance, beginning of period	71	0	60	14
Net gains (losses) included in net income	0	(1)	0	1
Net gains (losses) included in other comprehensive income	0	0	0	0
Purchases, sales, issuances and settlements, net	(3)	0	8	(16)
Transfers into Level 3	0	21	37	21
Transfers out of Level 3	(56)	0	(93)	0
Balance, end of period	12	20	12	20
Net unrealized gains (losses) included in income related to assets and liabilities held at period end	0	0	0	0
Loans [Member]
Assets:
Balance, beginning of period	225	352	244	376
Net gains (losses) included in net income	1	0	1	(1)
Net gains (losses) included in other comprehensive income	0	0	0	0
Purchases, sales, issuances and settlements, net	(24)	(31)	(43)	(54)
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Balance, end of period	202	321	202	321
Net unrealized gains (losses) included in income related to assets and liabilities held at period end	(2)	(4)	(4)	(7)
Mortgage servicing rights [Member]
Assets:
Balance, beginning of period	13,336	15,041	14,649	13,625
Net gains (losses) included in net income	(1,639)	(115)	(3,012)	732
Net gains (losses) included in other comprehensive income	0	0	0	0
Purchases, sales, issuances and settlements, net	399	485	459	1,054
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Balance, end of period	12,096	15,411	12,096	15,411
Net unrealized gains (losses) included in income related to assets and liabilities held at period end	(1,078)	345	(1,969)	1,675
Derivative [Member]
Assets and Liabilities:
Balance, beginning of period	(46)	(278)	21	(378)
Net gains (losses) included in net income	177	(90)	209	(350)
Total net gains (losses) included in other comprehensive income	0	0	0	0
Purchases, sales, issuances and settlements, net	(133)	18	(211)	329
Transfers into Level 3	(2)	3	9	3
Transfers out of Level 3	(13)	2	(45)	51
Balance, end of period	(17)	(345)	(17)	(345)
Net unrealized gains (losses) included in income related to assets and liabilities held at period end	106	258	46	(17)
Derivative [Member] | Interest rate contract [Member]
Assets and Liabilities:
Balance, beginning of period	101	(8)	25	71
Net gains (losses) included in net income	237	(63)	424	(408)
Total net gains (losses) included in other comprehensive income	0	0	0	0
Purchases, sales, issuances and settlements, net	(133)	30	(244)	296
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Balance, end of period	205	(41)	205	(41)
Net unrealized gains (losses) included in income related to assets and liabilities held at period end	141	6	220	(94)
Derivative [Member] | Commodity contract [Member]
Assets and Liabilities:
Balance, beginning of period	(18)	10	4	19
Net gains (losses) included in net income	(75)	15	(126)	30
Total net gains (losses) included in other comprehensive income	0	0	0	0
Purchases, sales, issuances and settlements, net	64	(2)	91	(26)
Transfers into Level 3	0	3	2	3
Transfers out of Level 3	0	0	0	0
Balance, end of period	(29)	26	(29)	26
Net unrealized gains (losses) included in income related to assets and liabilities held at period end	(10)	21	(26)	22
Derivative [Member] | Equity contract [Member]
Assets and Liabilities:
Balance, beginning of period	(162)	(322)	(17)	(511)
Net gains (losses) included in net income	15	(12)	(104)	57
Total net gains (losses) included in other comprehensive income	0	0	0	0
Purchases, sales, issuances and settlements, net	(66)	(7)	(69)	64
Transfers into Level 3	(2)	0	7	0
Transfers out of Level 3	(13)	2	(45)	51
Balance, end of period	(228)	(339)	(228)	(339)
Net unrealized gains (losses) included in income related to assets and liabilities held at period end	(29)	261	(175)	80
Derivative [Member] | Foreign exchange contract [Member]
Assets and Liabilities:
Balance, beginning of period	(16)	1	(26)	7
Net gains (losses) included in net income	3	(18)	10	(25)
Total net gains (losses) included in other comprehensive income	0	0	0	0
Purchases, sales, issuances and settlements, net	3	2	6	3
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Balance, end of period	(10)	(15)	(10)	(15)
Net unrealized gains (losses) included in income related to assets and liabilities held at period end	7	(13)	17	(17)
Derivative [Member] | Credit contract [Member]
Assets and Liabilities:
Balance, beginning of period	49	41	35	36
Net gains (losses) included in net income	(3)	(12)	5	(4)
Total net gains (losses) included in other comprehensive income	0	0	0	0
Purchases, sales, issuances and settlements, net	(1)	(5)	5	(8)
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Balance, end of period	45	24	45	24
Net unrealized gains (losses) included in income related to assets and liabilities held at period end	(3)	(17)	10	(8)
Other liabilities [Member]
Liabilities:
Balance, beginning of period	(2)	(2)	(2)	(3)
Net gains (losses) included in net income	0	0	0	1
Net gains (losses) included in other comprehensive income	0	0	0	0
Purchases, sales, issuances and settlements, net	0	0	0	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Balance, end of period	(2)	(2)	(2)	(2)
Net unrealized gains (losses) included in income related to assets and liabilities held at period end	$ 0	$ 0	$ 0	$ 0